Theodosius II and Valentinian III ( ruled 425 â `` 450 ) , repaired damage caused by an earthquake in 443 ; more work followed in 484 and 508 . An inscription records the restoration of various parts of the Colosseum under Theodosius II and Valentinian III ( reigned 425 â `` 455 ) , possibly to repair damage caused by a major earthquake in 443 ; more work followed in 484 and 508 .