The Horseman Stable is a Bronze Age Military Building. It is where a player can train the Horseman, the fast unit of the age. It is the third unlocked military building of the age. In order to construct a Horseman Stable, a player needs to have unlocked the Horseback Riding technology.
It is not recommended to build the Horseman Stable because the Horseman is not very effective in the Bronze Age.
The Horseman is most effective against ranged units. Horsemen have no terrain bonus and cannot travel through rocks.
For more information about the military unit, visit the Horseman page.