Captive warriors known for their virility were chained to an altar at the Temple of Priapus, the god of fertility. Their daily sperm contribution was believed to bring abundant crops to the village. Some shot their loads spontaneously others needed a helping hand. Some needed the threat of a sword held above them. Their lives were safe as long as they could shoot a daily load.
The notion of a fertility god is hot.
Of course, even the most virile of captured warriors will eventually play out and begin to dry-cum on the altar. At that point his usefulness will have ended. After he has been put to the sword, the prisoner's spent cock and balls will become nourishment instead for the carrion birds circling watchfully over Priapus. But never-ending wars and abundant captives from among the vanquished guarantee replenishment of the altar with a constant supply of throbbing meat.