» For the brand of bicycle tubing, see Reynolds 531. Events By Place Byzantine Empire April 19 — Belisarius is defeated at the Battle of Callinicum; Mundus briefly takes command of the army. Some members of the Blue and Green chariot racing factions in Constantinople are imprisoned for murder, precipitating the Nika riots the next year. The building of St. Sophia Basilica, Constantinople, is begun, and is completed in 537. Europe Theudis succeeds Amalaric as king of the Visigoths.… (More on 531)