Hercules and the Princess of Troy (1965) on Netflix

Plot summary

Hercules is aboard the Olympia when he comes upon a ship whose Trojan passengers are being held by pirates, and he frees them. Their city lives under a demand: once a month a maiden is handed to a sea monster, or the creature destroys Troy, and families who try to leave are seized at sea. In Troy, Hercules is given the use of two horses that arrows cannot wound, and Ortag tells him that the monster's armor leaves its belly open. Princess Diana is heir to the throne that her uncle Petra holds. Hercules, with Ulysses and Diogenes, faces both the creature and Petra's warriors.