August 18, 293 BC The oldest known Roman temple to Venus was founded, starting the institution of Vinalia Rustica (festival sacred to Jupiter). 328 Saint Helena, the mother of Roman Emperor Constantine the Great, died at age 82. 1201 The city of Riga(Baltics) was founded, and became a thriving center of Viking trade. 1227 Genghis Khan, the great Mongol conqueror, died at age 60. 1572 The future Huguenot King Henry IV of Navarre was married to Marguerite de Valois, in a supposed attempt to reconcile Protestants and Catholics.