Although Metastasio set the plot in ancient Numidia, the original story had nothing to do with the historical Syphax and was actually about king Peter of Castile, based in an account in volume four of the fifteen volume "Historia della perdita e reaquisto dell Spagna accupata da Mori (Story of the loss and recovery of the Kingdom of Spain occupied by the Moors)" by Bartolomeo de Rogatis.