The Legionnaire Barracks is an Iron Age Military Building. It is where a player can train Legionnaires, a heavy unit of the age. It is the fourth unlocked military building of the age. In order to construct the Legionnaire Barracks, a player needs to have researched the Chain of Command technology.
It is highly recommended to build the Legionnaire Barracks, as Legionnaires are very useful against the Soldier, a common unit of the Iron Age.
More information can be found on the Legionnaire page.
In update 1.85, the graphic of the Legionnaire Barracks was reworked.