Was playing a Pitboss game the other day when my Scout noticed that the AI had built a corral on what appeared to be empty terrain.

It was early in the game, and NO Civ had access to Horses (as a resource).
Sure enough, later in the game, horses had found their way into this corral.

Cheers
Gryphyn

They can't build pastures if they don't know Animal Husbandry. My guess is that the AI indeed had AH but you didn't so you couldn't see the Horses. If it was very early in the game, the AI has probably acquired AH from a tribal village.

They had animal husbandry but you didn't, and hence could see the horses when you couldn't. No bug here.