They Are Billions: Colony Defense and Survival Guide

Surviving in They Are Billions isn’t just about building walls and hoping for the best—every decision counts, from where you place your first tent to how quickly you expand your defenses. With waves of infected threatening to overrun your colony at any moment, the pressure never really lets up. It’s a game that tests your planning, adaptability, and nerves, and even experienced players can find themselves caught off guard. Whether you’re aiming to last just one more day or hoping to see your colony thrive against impossible odds, understanding the core strategies behind defending your settlement makes all the difference.

Wall and Gate Placement

Wall and gate placement separates seasoned survivors from casualties in They Are Billions. Simple barricades won’t hold back the infected for long, so where and how you structure your defenses makes a major difference in how long your colony lasts. This section breaks down best practices for wall and gate use, from early scraping by to late-game strongholds.

Understanding Wall Types and Their Use

Walls come in two main varieties: wood and stone. Each tier offers more hit points and resistance to those relentless zombies. Early on, wood walls are your go-to because they’re cheap and available right away. However, their low durability means the infected can chew through them fast if you’re not careful. Once you upgrade to stone, you get a sturdier barrier that can buy you the time you need to mobilize defenses or repair.

Think of walls as your first line of damage control. They won’t kill the infected, but slowing them down is often all you need to pack more of a punch with defensive units or traps.

Single vs. Double Layer Walls

A single layer works fine for small groups of infected or the early days, but investing in double (or even triple) layers multiplies your chances of holding off a breach, especially during special swarm events. For best results, leave at least one tile of space between layers. This spacing makes it harder for splash damage (for example, from Harpies or Chubby special infected) to take out multiple layers at once.

Key Placement Strategies

Choke Points Are Your Friends

Scan the edges of your buildable area. Natural barriers—things like lakes, cliffs, or forests—block infected movement and reduce the space you have to guard. Place walls where the enemy must pass: fill in the gaps between these obstacles rather than trying to encircle your entire base. Fewer wall segments mean less to maintain, and your troops can focus fire where it matters most.

Wrapping Villages and High-Value Structures

Put extra defensive layers around housing and key resource buildings like the Command Center, warehouses, and power plants. If a fence gets breached, you’ll want time to rally units. Gates here should be rare; every access point is a risk.

Where (and When) to Place Gates

Gates give your units a way to cross defenses easily, but every gate is weaker than a solid stretch of wall. Too many and you’re basically installing “break here” signs for the zombies.

Gate Placement Tips

• Place gates at convenient paths for your patrols or for resupplying outposts, but avoid making straight lines from gates to the Command Center.
• Only use gates where absolutely necessary. If you can, use soldiers posted behind walls and use the “hold” command instead.
• Always reinforce gates with overlapping towers and a thick cluster of traps or overlapping fields of fire.

Wall Maintenance and Upgrading

Don’t just set it and forget it. As your colony grows, so do attack waves. Keep tabs on where past breaches happened—those spots deserve thicker walls and added traps.

Upgrade wooden walls to stone as soon as you have the resources, especially at choke points. Repair any damage after a wave. Even a single missing wall section can mean disaster when the next infected swarm arrives.

Advanced Tactics: Funneling and Killzones

You can “funnel” infected into certain paths by strategically shaping your walls. Use long, narrow passages (with double or triple walls on the sides) leading into a cluster of traps and gun emplacements. These killzones force hordes to bunch up, making them easy targets for your firepower and maximizing the impact of traps.

Example Basic Layout

• Natural obstacle - wall - wall - gate - wall - natural obstacle
• Behind the wall: Ballista or executor towers pointed right at the gate area.
• Stagger traps so any breach slows infected even once they’re inside.

Common Mistakes to Avoid

• Stretching walls too thin by trying to wall off too much area.
• Forgetting to double-wall or reinforce gates and main entrances.
• Not watching corners or wrapping your economy buildings.

Summary

Smart wall and gate placement isn’t flashy, but it’s one of the main reasons colonies survive the late game. Use natural barriers, layer up where needed, and treat every gate as both a vital access point and a potential liability. Invest in your defenses—not just with walls, but by making sure those walls work for you. With a good layout, your units can hold back even the roughest hordes, buying your colony those precious extra days.

Defensive Structures: Choosing and Upgrading Towers

Towers carry a lot of weight in They Are Billions. The infected swarm in huge numbers, and firing lines alone can't cover every angle for long. That’s where defensive towers come in—providing a strong, elevated position for your soldiers or unleashing automated fire at advancing enemies.

List of Key Defensive Structures

• Wooden Towers: The first tower type available and a quick way to improve soldier range and vision. Place these where you need cost-effective coverage early in the game.
• Ballista Towers: Unlocked after researching at the Wood Workshop. Ballistas are your early anti-horde tool, with solid damage and splash potential—just don’t rely on them alone for late game.
• Stone Towers: Provide an upgraded firing position. Soldiers inside shoot farther and see more, keeping your critical buildings protected from sudden snipers or Harpy leaps.
• Executor Towers: These are the big guns. Extremely expensive, but with ruthless stopping power and splash damage. Place Executors at major choke points by the mid-late game, especially along high-traffic parts of your walls.

Upgrading Towers: When and Why

Don’t rush to spam the fanciest tower everywhere—resources are scarce. Upgrade only at high-pressure areas or breach-prone zones. A well-placed Executor can clear dozens of infected in seconds; stacking them in key places is smarter than covering every inch with Ballistas.

Balancing upgrades and expansions is key. Improve towers where past attacks have concentrated, but don’t upgrade low-threat flanks unless things change.

Placement Tactics: Maximizing Firepower

Where you drop your towers is just as important as what you build. Every tile counts.

Overlapping Fields of Fire

Never rely on a single tower to protect a wall section. Stagger your towers so their firing arcs overlap. This way, if one gets destroyed or overrun, the next picks up the slack—giving another crucial second to repair or reinforce. You should be able to see crossfire over major gates and choke points.

Elevated Positions

Soldiers and snipers stationed in towers get an attack and range boost. Prioritize tower placements behind your thickest walls and killzones, or in places where their line of sight covers key resources. Stone towers, in particular, paired with snipers or Thanatos, create a formidable anchor that slows tough infected like Chubbies and Mutants.

Protecting Your Towers

Towers are just as much a target as the walls in front of them—sometimes more so. Don’t position all your towers flush with the outer wall. A common trick: leave one or two tiles between the tower and the wall, forcing zombies to breach the wall before damaging your firing platform. Back towers with more traps or extra double walls in weak areas.

Supporting Towers with Traps

Towers and traps work together, especially when you’ve funneled zombies into a tight area. Start with wooden traps (easy and cheap), then switch to stakes and wire traps later on. Line your killzones with traps, slowing infected and letting towers mop up crowds.

Trap Strategies: Slowing and Softening the Horde

Traps aren’t flashy, but they’re a lifesaver against the masses. Here’s a quick runthrough on how to use them well:

• Wooden Stakes: Slow and damage the first waves. Cheap, but don’t last forever.
• Wire Fences & Oil Traps: Later in the game, switch to stronger traps that deliver better crowd control.
• Lay traps in staggered rows rather than thick clusters—this spreads out the effect, burning time and hitpoints as the swarm surges forward.
• Traps directly in front of gates buy you a little extra time for reinforcements.

Adapting Defense: Reading Threat Levels

Attack timing and direction aren’t random. Notice where zombies attack after each wave—sometimes the game “picks” a weak spot, and then hits it repeatedly as days pass. Use patrols and towers to scout upcoming threats and react fast.

If you spot a wave gathering somewhere unexpected, drop new towers and traps even if it means scrapping plans in a safe area. Remember: a handful of towers and soldiers in the right place is better than a thin spread everywhere.

Tower Defense in the Endgame

Late-game waves demand the best defense you can muster. Stack strong towers (Ballistas, Executors) at the four sides of your colony, with choke points layered with triple walls, traps, and overlapping fire. Leave extra units inside your walls for emergencies—they can dash out if a tower or gate falls.

Don’t be afraid to pause and rebuild during quiet spells. Getting caught without enough towers, especially on brutal Apocalypse difficulty, ends most runs in a matter of seconds.

Pro Tips for Tower Defense Success

• Always keep a few shock troops (Thanatos, snipers, or even Titans) stationed near tower clusters for manual response.
• Mix unit types: place a couple snipers for range, soldiers or Thanatos for splash, depending on your expected threats.
• Use the pause button before a wave hits to tweak tower placement and trap lines.
• Never let a breached area go unfortified; patch it up better than before.

Final Thoughts

Fighting off the billions isn’t about just spamming defenses everywhere—it’s about smart, layered design. Prioritize overlapping fire, use chokepoints, support every tower and gate with traps, and pay attention to threats as they change. With thoughtful tower defense, your colony stands a real shot at seeing the final day. Unit composition can make or break your colony in They Are Billions. No matter how tough your walls or how well-placed your towers are, the mix of units defending them determines whether a zombie rush fizzles out or punches through everything. Here’s everything you need to know to pick, train, and position units for every phase of the game.

Understanding Unit Roles

The Starting Units: Rangers, Soldiers, and Snipers

Each basic unit has a purpose, and how you balance them early sets you up for mid-game stability—and, ultimately, survival.

Rangers

• Speedy and Silent: Rangers are fast on their feet, have a quiet attack, and cost the least to produce.
• Early Scouting and Kiting: Use them to scout map edges, lure small packs, and run circles around slow zombies. Their low noise means fewer accidental pulls.
• Weak in Defense: Not tanky and do less damage than late-game units. Replace them on the front lines as soon as you can.

Soldiers

• Bulky, Reliable Damage: Soldiers pack more health and hit harder. Their guns, though, are loud, pulling bigger waves if you’re not careful.
• Frontline Holders: Put them where you expect sustained pressure—gates or breach-prone sections.
• Good All-Rounders: Hold out longer than Rangers, but upgrade to heavier units ASAP when swarms get nasty.

Snipers

• High-Powered, Long-Range: Snipers shoot slow, but every hit usually drops a target. Perfect for thinning out special infected and picking off Chubbies or Harpies before the rest of your crew chews through fodder.
• Ideal for Towers: Always stash them in stone towers or bunkers for maximum range. Back them up with distractions or meatier units, since they’re not speedy or tough.

Specialized Units: Thanatos, Lucifers, Titans

Once you move beyond the basics, your squad options expand, letting you muscle through the horde with sheer firepower and specialized abilities.

Thanatos

• Rocket Crowd Control: Fires rockets with splash damage, devastating clusters of zombies.
• Slow but Brutal: Has low movement speed, so use at chokepoints or behind walls. Pair with snipers for reach and splash.
• Perfect Panic Button: Keep a few in reserve for breaches—they clear rooms fast.

Lucifers

• Flame Specialists: Sprays a cone of fire, burning masses of infected at close range.
• Thick Armor, Fast Heal: Tough enough to patrol your perimeter. Their close-range focus means they're ideal for plugging small holes.
• Watch Out: Can’t attack through walls or shoot from towers—needs open lines.

Titans

• Ultimate Offense & Defense: Expensive to train, but unmatched at soaking up damage and shredding through just about anything.
• Autonomous Sweepers: Use them to patrol trouble spots mid/late game.
• Resource Intensive: Don’t overcommit early—they’re an endgame luxury.

Balancing Your Army

Early Game: Flexibility and Field Coverage

You won’t have the resources for fancy units right off the bat. Focus on producing enough Rangers for map control, then slowly swap for Soldiers as gold and food flow in. One or two snipers per flank help pick off runners and specials.

Tips

• Assign hotkeys or control groups to your scouts so you can respond quickly to breakouts.
• Don’t cluster all units together—spread them to maximize sight lines and reaction time.

Midgame: Layered Defense

By this point, you want a mix. Upgrade outer defenses with Soldiers and Snipers, especially near gates. Start reserving resources for Thanatos and Lucifers. Mix snipers with every group. They can thin crowds before melee units even fire a shot.

Tips

• Place Thanatos at killzones where multiple walls and traps slow infected.
• Use Lucifers to patrol internal streets—especially after a breach, they’re fast at mop-up where towers can’t reach.

Late Game: Heavy Hitters and Specialized Support

Endgame waves force you to bring out the big guns. Fill towers with snipers, line walls with Thanatos, and drop Titans near high-risk flanks or open sections. Leave Lucifers free for rapid response when swarms slip past.

Tips

• Overlapping fields of fire matter even for mobile units—arrange them to support each other.
• Use pause before a wave to redistribute units in anticipation of attack direction.
• Always keep one or two reserves (Thanatos or Titan) to throw at sudden breaches.

Unit Synergy: Combining Strengths

You don’t want to fill your front line with just one unit type. Mixing it up is the only way to handle the wide variety of infected the game throws at you.

• Sniper + Thanatos: Snipers pick off tough targets and whittle crowds; Thanatos handle clusters that rush the wall.
• Soldier + Lucifers: Soldiers man the barricades, Lucifers nuke leaks or break-ins.
• Towers + Mobile Units: Back up tower chokepoints with a mobile squad behind in case the line fails.

Supporting Your Army

Don’t forget the backup needed for your squads. Build enough housing, food production, and gold income to keep new units flowing. Space out your recruitment buildings so you can reinforce multiple fronts simultaneously. Losing a hammer unit or two late game is painful unless you have a replacement lined up.

Adapting to Threats

Always pay attention to the specific types of infected heading your way. Swap out a few snipers for more Thanatos if runners start to overwhelm. If Harpies or spitters show up, prioritize quick firepower or high health units for dealing with them.

Final Thoughts on Unit Composition

A solid army in They Are Billions isn’t about maxing out just one type of soldier. It’s about choosing the right mix for each phase, stationing them wisely, and always keeping a few on hand for desperate moments. If you keep your composition balanced and respond to threats quickly, your colony stands a good shot at making it through even the tensest late-game assaults. Resource management in They Are Billions isn’t just a side chore—it’s the backbone of your entire colony. Mismanage your resources, and even the strongest army or thickest wall starts to crumble. Let’s break down each type of resource, how to get it, and strategies for getting the most out of every bit you collect.

All the Resources You’ll Need

There are six core resources you’ll track constantly:

1. Food Needed to support more population and recruit units. Farms, Fishermen, Hunters, and Mills supply it.

2. Workers Provided by housing (Tents, Cottages, Stone Houses). Every advanced building, soldier, and machine eats up workers.

3. Wood Gathered with Sawmills placed near forests. Essential for early structures and expansions.

4. Stone Mined from stone outcroppings with Quarries. Required for sturdy buildings, walls, and advanced tech.

5. Iron Extracted from iron veins with Quarries. Costs spike fast when you tech up, especially for soldiers, Thanatos, and Titans.

6. Gold Generated by population (from houses), selling resources at the Market, and advanced buildings. Used for almost everything.

7. Oil Collected once you get Oil Platforms—needed for the highest tier tech and units.

Let’s talk about balancing all this without tripping over a shortage or facing a production stall.

Planning Early: Don’t Get Bottlenecked

Scouting for Perfect Placement

Before you build, send Scouts or Rangers to uncover the map. Look for:

• Dense forests for wood.
• Rich patches of stone and iron.
• Open fields for farms.
• Water for fishing huts.

The sooner you know your map, the less likely you’ll be blocked from key upgrades down the road.

Don't Overcommit

Early on, it’s tempting to crank out units or spam buildings. If you do this without considering food and workers, you’ll suddenly find yourself unable to expand when a wave hits.

Pro Tip: Always leave yourself a buffer of workers and food so you can respond quickly to problems.

Food: The Hidden Limit

Keeping Up Production

Every new house, soldier, and even most advanced buildings eat up food. Early on, mix Fisherman and Hunter Cottages for quick boosts. As soon as possible, switch to Farms—they’re more efficient and don’t compete for the same spaces.

Hot Tips

• Farms work best on grass; don’t waste green tiles on other stuff.
• Mills and advanced power buildings don’t take food, so they can be placed anywhere that isn’t prime farmland.

Workers: Always in Demand

Expand Housing

The more power you have, the more tents and cottages you can build. Upgrade early to Cottages, then Stone Houses as your resources permit, since each takes up only a little more space but gives way more workers.

Keep in mind

• Every building and unit type lists how many workers it needs. Queue up too much at once and you’ll grind to a halt.

Tip: Place houses in tight grids to maximize space and stretch out your territory a bit for more farm and quarry room.

Wood, Stone, Iron: The Building Blocks

Smart Resource Sites

Place Sawmills and Quarries near the richest spots possible. Sometimes shifting a building just one square gives a big jump in output (hover to preview before placing).

• Wood is always helpful, especially early—never let production drop off, or you’ll struggle to build walls and outposts.
• Stone is your next bottleneck; you’ll need it for defensive walls, towers, and key upgrades. Don’t neglect it once you secure your first patch.
• Iron gets needed in bulk for top-tier units and buildings. Expand toward new iron outcrops as you progress—never just rely on your starting one.

Gold: The Lifeblood

Reliable Income

Your gold tick comes from houses and certain late-game buildings (Banks, Markets). More people mean more gold—but only if you feed and shelter them.

• Sell surplus wood, stone, and iron at Markets for a quick cash boost, especially before a wave when you need an army in a hurry.
• Banks boost gold gathered by nearby housing—cluster them smartly.
• Don’t neglect expanding your housing zone if you want to up your gold ceiling.

Watch out: Troops and advanced buildings come with ongoing gold upkeep. Don’t bankrupt yourself or you’ll lose the ability to train troops when things get hot.

Oil: Endgame Catalyst

You’ll unlock oil later. The platforms take power, workers, and some setup, so plan ahead and station troops nearby (infected love to chomp undefended platforms). Titans, Thanatos, and Wonders eat up oil in big amounts, so keep expanding capacity as you move through the tech tree.

Timing and Expansion

Don’t Rush Upgrades

There’s always a temptation to jump to stone walls or Titans as soon as possible. Instead, build up a surplus buffer of each resource so you can still react to emergencies.

• Expand to new resource spots when safe, pushing forward with your army.
• Always leave a reserve so you’re not caught short during a sudden attack.

Map Control and Resource Denial

Keeping zombies at bay isn’t just about safety—it also gives you room to harvest resources and deny late-game choke points to the infected. Fence off quarries, set up patrols, and clear out key farmlands quickly.

Common Mistakes (and Fixes)

• Under-producing food: Leaves you stuck; always keep an eye on your food bar.
• Letting worker count hit zero: Suddenly, nothing gets built and no troops spawn. Ugh.
• Forgetting to expand power: If you run out of power, you can’t place new buildings. Always follow up every expansion with a power plant or mill.
• Wasting prime farmland: Don’t block grassland with sawmills or quarries unless you have zero other options.

Final Thoughts on Resource Management

Mastering resources is what separates thriving colonies from the ones that fall apart after the fourth wave. Keep production steady, maintain extra food and workers, watch your gold, and defend your harvesters. Every time you secure a new patch of stone or farm, you’re one step closer to surviving when the hordes close in. Certainly! Here’s an in-depth and approachable guide section for Surviving Final Waves in They Are Billions.

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Surviving Final Waves

The closing waves in They Are Billions turn everything up to eleven. You’ll hear the foreboding warning horn, see thousands of infected moving at once, and realize this is what you built everything for. If your base prep falls short, the horde will rip through your colony in seconds. This section covers practical tactics, defense layering, and army placement tips to maximize your odds of survival.

Understanding the Threat

The last waves send every kind of infected at you—and lots of them. Expect harpies leaping walls, spitters attacking from a distance, and mutated giants stomping through weak points. The game usually announces where the main attack will hit, but near the finale, multiple sides become vulnerable. Don’t get tunnel vision; spread your attention and resources.

Fortifying Your Defenses

Double and Triple Walling

Single walls won’t cut it. By the final days, layer your walls in rows—ideally three layers deep in high-risk spots. Space them so there’s room for traps and shock towers between each layer. Use stone for the first line, then wood/stone for backup, and reinforce with towers behind each. Repair damage between waves—don’t wait until it’s too late.

Choke Points and Maze Building

Funnel the zombies with choke points. Even if you have a wide wall, try creating tight entrances or curved corridors leading up to your defenses. Fill these with traps (spikes, wire traps) and place your firepower at the end. A simple zig-zag or right-angle corner makes zombies bunch up, allowing AoE units to do more work.

Towers and Turrets

Line the front with Executor turrets—they hit hard, have a great fire rate, and can hold a spot much longer than Soldiers or Rangers alone. Place Thanatos around these for splash damage; their rockets wreck big crowds, especially when zombies bunch up. Don’t sleep on Shock Towers: they’re amazing at overlapping paths and corners, just watch the power drain.

Trap Placement

Landmines and spike traps aren’t just early-game luxuries. Restock them between waves, focusing on the most targeted gates and choke points. Layers of traps slow down and soften up even the biggest brutes. Consider adding wire traps at the last line in case runners break through.

Army Composition and Unit Control

Unit Mix

Rangers and Soldiers are too weak late-game, except for patrol duty. Your final defense should focus on:

• Thanatos: Best crowd control with their rockets.
• Titans: Tanky, great at mowing down endless regular infected, but less effective against giants.
• Lucifers: Use cautiously—powerful short-range flamers, but vulnerable if swarmed or if walls fall.
• Snipers: Great for picking off "specials" behind the main horde—but don’t use them alone.
• Executors: Your backbone. These turrets melt nearly anything up close.

Mix and match units so each key section of your wall has at least AoE damage (Thanatos, Lucifer), hard hitters (Snipers), and adequate range coverage. Titans and Lucifers shine outside the walls as "mobile clean-up"—pull them back if a breach happens.

Positioning

Stack your units behind walls, but don’t huddle them all in one spot. Reserve some anti-special shooters (Snipers) for backup rows. If a breach happens, move Titans and Lucifers to plug holes—they don’t get stuck on rubble as easily as infantry.

Hot Tip: Set patrol routes behind far walls for your fastest units in case zombies break through. You don’t want your army trapped in towers as the base falls apart.

Adapt When Things Go Wrong

Rapid Repairs

As soon as walls or towers start taking hits, use the repair hotkey—don’t wait for wave lulls. It’s easy to miss this when you’re juggling multiple fronts, but even a few seconds of extra wall health buys time for backup units.

Contingency Plans

Have backup power lines and backup walls around critical structures like your Command Center and housing districts. The final infected push will chunk through your outer layers. Once the walls go, build new lines behind using quick stone or wood placements, and immediately move army units to intercept. Sacrifice non-critical buildings (like Mines or random Warehouses) to save your Command Center.

Managing Panic

The biggest threat in late waves is cascade failure—one breach leads to an avalanche. Pay attention to audio cues (where are the groans loudest?) and mini-map indicators. Quickly triage the most threatened section and shift reinforcements, even pulling from less-threatened walls if you have to.

Final Hours Checklist

• Repair all walls and traps before the final waves hit.
• Reinforce gates and choke points with extra turrets, walls, and overlapping fields of fire.
• Retrain lost units/stockpile replacements in advance.
• Double-check all resource production is safe or expendable—last waves don’t need long-term economy.
• Save the game a few waves before the final battle in case you need a do-over.

Surviving to the End

Making it through the final assault is about preparation, smart base design, flexible unit control, and knowing when to shift your focus on the fly. Don’t panic if things start falling apart—it happens, even to veteran players. Sometimes success means surviving with just your Command Center and a handful of battered units. If you make it to the end screen, you’ve earned it.

Keep these late-game habits in mind, and every playthrough will teach you something new—even if the swarm wins now and then. Good luck!