The Princess and the Pirates (SPQR)

His two years of aedileship over, Decius is ready for his next adventure. He would rather do anything than join the war with Caesar, so he and Hermes find themselves on a mission to rid the Mediterranean of pirates. They set off with shoddy ships and sailors to the island of Cyprus, where a young Cleopatra is staying. Between her impressive crew and the ex-pirate Ariston providing insider knowledge of that cutthroat occupation, Decius thinks he stands a good chance of bringing himself some glory.

That would be too simple though. The ruler of the island is murdered and Decius has a sacred duty to find and punish the guilty party. As he investigates world trade, the island history, and the new kind of piracy plaguing the waters, he is finding connections more menacing than he had ever imagined possible.
Roberts crafts another skillful mystery, this one fervently pulsing with the collision of Roman, Greek, and Egyptian interests.