How would a medieval army conquer a treetop city?

Question

In my book series, an evil space conqueror named Tate is attacking the planet of Aztlan. However, in order to do so, he must subjugate the Avian tribe and their capital city of Palo Alto. However, there is one problem: Palo Alto is built in the treetops of Cloudburst Forest. How would Tate and his army reach this treetop city, defeat the Avians, and conquer it?

Some things to note about Palo Alto:

• The city is built on the treetops of Cloudburst Forest
• The city bears a strong resemblance to the Ewok village from Return of the Jedi, but is a city of 150,000 people instead of a tiny village
• The only way up to the city is a narrow spiraling ramp up a tree that is guarded by the lion's share of Palo Alto's troops

Some things to know about Aztlan in general:

• Planet's culture and technology is based on Aztec, Incan, and Mayan civilizations
• The planet is home to Aztec animals and wild dinosaurs (the ones that have been domesticated for war purposes will be mentioned when I talk about armies and army sizes)
• Tate is on Aztlan trying to steal the souls of the Lords of Xibalba to use them in his dark ritual. However, he has no idea where they are, so he has to torture the information out of people like the King of the Avians.

Some things to know about Cloudburst Forest:

• The forest is dominated by mutant kapok trees that are double the size of giant sequoias. These trees' bark is coated in a special magical salve (made mostly of coconut milk enchanted by Aztlan's Black Sun Priestesses) that makes them nigh indestructible. The city of Palo Alto is built on these.

• The forest is surrounded by impenetrable mountains in all directions but the east. On the east is Zultun Dock, an area the Avians use as a harbor on Lake Coxcote (which is east of Zultun Dock). The Tatians control Zultun Dock, as well as the eastern half of the forest floor.

• The ramp to Palo Alto is located at the western edge of Cloudburst Forest. Here, a large waterfall coming down from the cliffs to the west feeds a stream that bisects Cloudburst Forest and flows into Lake Coxcote. At the bottom of this waterfall, there is a small island with a single tree on it. This tree has a spiral ramp carved into it that serves as the only ground entrance to Palo Alto. It is guarded by the majority of the Avians' forces. The western half of the stream is guarded by Avian canoes. Around 1/3 of the Avians remain in Palo Alto itself in case all else fails.

• Stats for Avians:

• Troop numbers: 24,000 Avian Infantry, 12,000 Avian Archers, 5,000 other Aztlanian Infantry, 4,000 Cavalry (Utahraptor riders), 100 War Canoes (each war canoe contains a rower, an archer, and a warrior).

• Weapons: Avian Archers use bows/arrows, slings, blowguns, and atlatls. Avian Infantry use macuahuitl. Other Aztlanian Infantry use similar weapons to the Avian Infantry. The cavalry rides on Utahraptors and uses tlacochtli spears.

• Stats for Tatians:

• Troop numbers: 20,000 Aztlanian Mercenaries, 8,000 Aztlanian Archers, 14,000 Squidian Mercenaries, 3,000 Squidian Archers, 13,500 108er Mercenaries, 4,000 108er Archers, 200 Vigamian Mercenaries, and 40 Vigamian Archers. Roughly 2/3 of each mercenary group are infantry, and the other 1/3 are archers. The one exception are the 108ers, which are split evenly between infantry, archers, and sailors. Squidian cavalry is zebra-based, and 108er cavalry is mostly horse-based, though they did bring 20 war mammoths. Vigamian cavalry rides gigantic milipedes the size of small cars.

• Weapons: Aztlanian Mercenaries use the same weapons as the Avian troops. 108ers are basically space vikings, using viking broadswords, chainmail armor, great axes, bows/arrows, and wooden shields. Squidians use African weapons, such as the Iklwa spear, Zulu shield, scimitar, Kpinga, and Makrigga. Vigamian troops use broadswords, scythes, plate armor, clubs, boomerangs, and daggers. The 108ers have built ~600 longships, which are stationed at Zultun Dock. The archers for each mercenary group (except the Aztlanians) all use basically identical bows and iron-tipped arrows.

Other important context

• Although both sides of this battle are capable of space travel, their spaceships are magic-powered instead of tech-powered, so space travel does not give any side a technological edge

• This battle takes place well after the Tatians have already landed their ships, and those ships are on the other side of the planet, so they cannot attack from the air.

• If you need to know more about this universe's magic system, click here.

• If you need to know more about this universe in general, click here.

• If you need to know more about Aztlan, click here.

Victory Conditions

• Tate: get the Avian king to surrender and tell him where to find the Lords' souls. City does not need to be intact because he's just going to blow up the planet anyway during his ritual, but he's not going to go out of his way to destroy the city or anything

• Avians: survive long enough for the Tatians to decide to give up

Answer 1

The traditional way would be to get your people into the tree tops and just fight them. You could do this in many ways. Fling ropes or grappling hooks into the branches. Use a ladder to get into the branches, just fight you way in, etc etc. I think these are all boring so lets get more creative.

Smoke and Fire. The problem with living in a forest is a forest fire. You have indestructible trees but there is still a lot of plant matter in the forest. Grass, weeds, fallen leaves, fallen trees are all fuel to start a fire. With a good breeze, the smoke will blow up into the village forcing them to flee. There is also the chance of trees burning. You can't really cover every tree because its a goddam forest and you certainly wont cover the trees from top all the way to the bottom (too resource intensive). If you can get a starting fire high enough, it could burn the unprotected parts of the trees as well as any wooden constructs in the tree tops. Once they are forced out of the tree tops, you hunt them down while their eyes are still watering and they are still coughing from the smoke.

Poison. The waterfall and lake sound like the main source of water for the Palo Alto. Poison it. Not something too serious, enough to make you get diarrhea (which means more water forming a cycle). Eventually, they will need to come out and fight you because they will run out of water. Another way would be to just make all your troops shit into the waterfall (or at the water falls source). As long as downstream it becomes undrinkable, your good to go.

Poison again. You could also poison the trees. They might be indestructible, but the roots of a tree need nurtriest and water, and so poisoning the trees bypasses your magic bark protection. Dead forest allows for easier pickings and can apply a huge amount of pressure onto the king. The idea of poison isn't to kill everyone. Its to make them suffer and understand that a slow and painful death is coming for them.

Finally, just destroy all the other places. This was brought up in Game of Thrones when Cerci saying they should hole up while the Dothraki invaded. Unfortunately, a capitol is dependent on surrounding cities and farm lands to sustain it. Just destroy the other ones. Eventually they will need to fight you. To save their people and their food supplies. Even better, allow a ton of survivors to escape and make them flood Palo Atlo for you. This puts more strain on their people and supplies and in the eyes of the people, its the kings inaction that is causing this.

Answer 2

Girdle the trees and wait.

Girdling is the technique of removing a ring of the inner bark near the base of the tree (to make trees die). Assuming these trees are like Earth trees, girdling will cause all of the trees to slowly die. Presumably, the inhabitants of the tree-city will have to evacuate their dying city sooner or later. This should put a clock on how long the city's inhabitants can withstand a siege.

Answer 3

Do what the Romans did and had been done up until the age of the canon:

Lay siege to it.

First, cut off the water supply. That aqueduct looks like a good first step.

Then either surround the trees at a safe distance (to prevent the Avians from simply dropping stuff on you) and prevent from getting to food and water.

Can the Avians fly? From the name, I would say yes but from some of what you said in the question, it is hard to tell.

This will work either way, it'll just be harder if they can fly.

If they can fly, then you have to place archers in the surrounding trees and shoot anyone attempting to leave.

Another method, you never said that they coated the leaves/needles of the trees. So, start a fire in the canopy. Even if their city doesn't catch fire, the smoke won't do them any good. It will also make it harder from them to sneak out of their city since the Avians will be easy to spot without the canopy growth.

Answer 4

Tate comes from space. That means he is coming from above, which is nice for bombardments, and has the technological advantage.

Tate can fight the birds the same way I fight wasps: expose their nests to some gas that keeps them from breathing. But unlike me, he needs some survivors, so just dose it down. Throw some canisters on the outskirts of the town only.

Also apply napalm to the surroundings of P.A. to keep food and help from coming in, and royalty from going out.

Once they surrender Tate can have a chat with them about souls.