- Cannot be built if Barracks has already been built in this district
A Stable offers the same bonuses as the Barracks, but boosts mounted units instead of infantry. It also becomes available a little later, at the beginning of the Classical Era. Note that you can't have both a Stable and a Barracks in the same Encampment!
Surprisingly, the Stable also gives 25% combat experience to all siege units, without explicitly stating so. This has been the case since the release of Civilization VI, but it is often unnoticed by players. Now, it can be easily confirmed by hovering your mouse over the icon on the unit panel, following the quality of life change introduced by the Civilization VI June 2019 Update.
What the barracks were for cavalry soldiers, stables were for their mounts. Indeed, the horses and mules of the military were generally better off than those peasants that took care of them. In most places, the stables also encompassed the barracks of the cavalry unit, from the Imperial Roman turma to Britain’s Household Cavalry. In addition to the stalls, mangers, feed storage rooms, grooms’ quarters (unless they slept with the horses), the military stables also provided large enclosures for training and drill, and of course there were the veterinarian’s quarters. In time, in some places such as England, the term “stable” even came to refer to the headquarters of a cavalry regiment. Besides the military stables of the land, there were often royal stables and mews, where the monarch’s personal mounts and carriages were kept; these usually had some form of mounted royal guard stationed within. Today, most cavalry stables have been replaced with the less glamorous “motor pools.”