You usually can’t go wrong with a flick in which warriors ride into battle on elephants, and yet this stolid and solemn slice of Thai history manages to make pachyderm cavalry — and bare-breasted amazons and multiple beheadings and bad omens and gruesome poisonings and invading legions and general palace intrigue — surprisingly dull. Filmmaker Chatrichalerm Yukol is a prince in the royal Thai family himself, and he based this grand, sweeping, boring epic upon actual events from 16th-century Thailand; perhaps he feared embarrassing his ancestors and figured he’d better keep us at a respectable distance from all the juicy stuff. A minor princess, Suriyothai (M.L. Piyapas Bhirombhakdi), marries the prince she doesn’t love rather than the one she does in order to prevent a rift in the kingdom, and things go downhill for her from there. There are too many kings, princes, consorts, regents, courtesans, wives, priests, and pretenders to keep track of and too many coups d’etat and civil wars to follow, and there’s no emotion in any of it. Yukol should have worried more about drawing us into the crimes and corruptions and passions of his ancestors, and less about upsetting their spirits.