"Build near Native settlements or Trade Routes. Provides experience points and other benefits."
The Trading Post is an economic/military building in Age of Empires III that replaces the old-fashioned trade system of carts, boats, and caravans in the previous games. Unlike most buildings, Trading Posts can only be built on a square-shaped site found on Trade Routes and minor civilization settlements. It periodically grants experience or resources if built on Trade Routes or allows access to native warriors and native technologies if built on minor civilization settlements.
It is sometimes possible for Trading Post sites to be generated on broken terrain, which means that players cannot construct a Trading Post on these sites. Most notably this can occur on the New England and Amazonia maps. This problem has been addressed in patches, occurring with less frequency.
Another common glitch is units getting stuck within the perimeter of a Trading Post as a result of trying to pass through it and not being able to get out. This most notably happens with Native Trading Posts. It is possible to destroy the units inside the confines of the Trading Post, but if an Explorer/Monk/War Chief get stuck inside, there is no way of removing them unless they can be ransomed.
If the player gets any building HP improvement such as the Improved Buildings or Advanced Trading Posts Home City Cards, already built Trading Posts remaining HP will stay the same as before the upgrade (e.g. 2,500/2,500 before, 2500/2875 after).
"Trading posts were established by early explorers of the New World as places to stop, barter, rest, and engage in commercial activities in support of their efforts to find wealth for their patrons, usually kings and queens, who sponsored their voyages.
Wealthy and powerful trading companies between the seventeenth and nineteenth centuries competed viciously as they drove exploration of the New World in search of pelts (chiefly beaver), to market in Europe. They dotted the landscape with trading posts and continued driving west in search of new sources of pelts. The fur trade and the need for the trading posts declined as fashions in Europe changed and the demand for pelts collapsed. Many trading posts developed into proper settlements over time."