Upper Mesopotamia had an established structure of dioceses by AD 500 following the introduction of Christianity from the 1st to 3rd centuries AD.[17] After the fall of the Neo Assyrian Empire by 605 BC Assyria remained an entity for over 1200 years under Babylonian, Achamaenid Persian, Seleucid Greek, Parthian, Roman and Sassanid Persian rule. It was only after the Arab-Islamic conquest of the second half of the 7th century AD that Assyria as a named region was dissolved.