At the beginning you should try to get a good economic basis. In order to do so you have to extend the 18 resource fields (village overview). There are four different types of resource fields: Woodcutter, Clay pit, Iron mine and Cropland. If you click one of them, you will get more information and the option to extend it.

Later in the game the buildings in the village become important too. In order to construct a new building you have to click on one of the green ovals. A list with every building that is available will appear.

Some buildings can only be built if you fulfil the prerequisites which are other buildings.

Main Building

The village's master builders live in the main building. The higher its level the faster your master builders complete the construction of new buildings.

Tribe advantage:
Romans: Can build/extend a resource field and a village building at the same time.

Costs and construction time for level 1:
70 | 40 | 60 | 20 | 2 | 0:33:20

Prerequisites:
none

Warehouse

The resources lumber, clay and iron are stored in your warehouse. By increasing its level you increase your warehouse's capacity.

Costs and construction time for level 1:
130 | 160 | 90 | 40 | 1 | 0:33:20

Prerequisites:
Main Building Level 1

Granary

The crop produced by your farms is stored in the granary. By increasing its level you increase the granary’s capacity.

Costs and construction time for level 1:
80 | 100 | 70 | 20 | 1 | 0:26:40

Prerequisites:
Main Building Level 1

Cranny

The cranny is used to hide some of your resources when the village is attacked. These resources cannot be stolen. At level 1 100 resources are hidden.

Tribe advantage:
Gauls: The cranny is twice as big.
Teutons: Enemy crannies only hides 66% of the normal amount in Travian version 2.5 and 3, and 80% of the normal amount in Travian version 3.5.

Costs and construction time for level 1:
40 | 50 | 30 | 10 | 0 | 0:12:30

Prerequisites:
none

Embassy

In order to join an alliance you need an embassy. With an embassy level 3 you can even found one yourself. With each higher level the maximum size of the alliance increases by 3.

Costs and construction time for level 1:
180 | 130 | 150 | 80 | 3 | 0:33:20

Prerequisites:
Main Building Level 1

Rally Point

At the rally point you can instruct your troops and can see the sender of oncoming troops. The rally point can only be build at the building site right of the village centre. The higher its level the more targets for the catapults become available.

Costs and construction time for level 1:
110 | 160 | 90 | 70 | 1 | 0:33:20

Prerequisites:
none

Marketplace

At the marketplace you can trade resources with other players. The higher its level, the more resources can be transported at the same time.

Tribe advantage:
Romans: Each merchant can carry 500 resources.
Velocity: 16 fields/hour.
Teutons: Each merchant can carry 1000 resources.
Velocity: 12 fields/hour.
Gauls: Each merchant can carry 750 resources.
Velocity: 24 fields/hour.

Costs and construction time for level 1:
80 | 70 | 120 | 70 | 4 | 0:30:00

Prerequisites:
Main Building Level 3, Warehouse Level 1, Granary Level 1

Barracks

Infantry can be trained in the barracks. The higher its level the faster the troops are trained.

Costs and construction time for level 1:
210 | 140 | 260 | 120 | 4 | 0:33:20

Prerequisites:
Rally Point Level 1, Main Building Level 3

Stable

Cavalry is trained in the stable. The higher its level the faster the troops are trained.

Costs and construction time for level 1:
260 | 140 | 220 | 100 | 5 | 0:36:40

Prerequisites:
Blacksmith Level 3, Academy Level 5

Workshop

Siege engines like catapults and rams can be built in the workshop. The higher its level the faster the units are produced.

Costs and construction time for level 1:
460 | 510 | 600 | 320 | 3 | 0:50:00

Prerequisites:
Academy Level 10, Main Building Level 5

Academy

New unit types can be developed in the academy. By increasing its level you can order the research of better units.

Costs and construction time for level 1:
220 | 160 | 90 | 40 | 4 | 0:33:20

Prerequisites:
Barracks Level 3, Main Building Level 3

Blacksmith

Your warriors' weapons are enhanced in the blacksmith’s melting furnaces. By increasing its level you can order the fabrication of even better weapons.

Costs and construction time for level 1:
170 | 200 | 380 | 130 | 4 | 0:33:20

Prerequisites:
Main Building Level 3, Academy Level 3

Armoury

Your warriors' armour is enhanced in the armoury's melting furnaces. By increasing its level you can order the fabrication of even better armour.

Costs and construction time for level 1:
130 | 210 | 410 | 130 | 4 | 0:33:20

Prerequisites:
Main Building Level 3, Academy Level 1

Palace

The King or Queen of the empire lives in the palace. The palace can only be built in one village at a time and can be used to make a village the capital. Capitals cannot be conquered.

At level 10, 15 and 20 three settlers or one administrator (Senator, Chief or Chieftain) can be trained.

The Capital is the only place a stonemason's lodge can be erected. Also the capital is the only village where resource fields can be extended beyond level 10.

Costs and construction time for level 1:
550 | 800 | 750 | 250 | 1 | 1:23:20

Prerequisites:
Embassy Level 1, Main Building Level 5, Residence

Residence

The residence is a small palace where the king or queen lives when he or she visits the village. The residence protects the village against enemies who want to conquer it as long as it is not destroyed.

At level 10 and 20 three settlers or one administrator (Senator, Chief or Chieftain) can be trained.

Costs and construction time for level 1:
580 | 460 | 350 | 180 | 1 | 0:33:20

Prerequisites:
Main Building Level 5, Palace

Trade Office

In the trade office the merchants' carts get improved and equipped with powerful horses. The higher its level the more your merchants are able to carry.

With each level the capacity increases by 10%. At level 20 your merchants can carry thrice as much as normal.

Tribe advantage:
Romans: In Travian version 3.5 the Roman trade office increases the capacity by 20% per level.

Costs and construction time for level 1:
1400 | 1330 | 1200 | 400 | 3 | 0:50:00

Prerequisites:
Marketplace Level 20, Stable Level 10

Tournament Square

Your troops can train to increase their stamina at the tournament square. The further the building is upgraded the faster your troops are beyond a minimum distance of 30 squares.

Costs and construction time for level 1:
1750 | 2250 | 1530 | 240 | 1 | 0:58:20

Prerequisites:
Rally Point Level 15

An elaborate building tree can be found at the Travian FAQ.