Heracles then had to herd the cattle back to Eurystheus. In Roman versions of the narrative, on the Aventine Hill in Italy, Cacus stole some of the cattle as Heracles slept, making the cattle walk backwards so that they left no trail, a repetition of the trick of the young Hermes. According to some versions, Heracles drove his remaining cattle past a cave, where Cacus had hidden the stolen animals, and they began calling out to each other. In others, Caca, Cacus' sister, told Heracles where he was. Heracles then killed Cacus, and according to the Romans, founded an altar where the Forum Boarium, the cattle market, was later held.