The first Armenian churches were built between the 4th and 7th century, beginning when Armenia converted to Christianity, and ending with the Arab invasion of Armenia. The early churches were mostly simple basilicas, but some with side apses. By the fifth century the typical cupola cone in the center had become widely used. By the seventh century, centrally planned churches had been built and a more complicated niched buttress and radiating Hrip'simé style had formed. By the time of the Arab invasion, most of what we now know as classical Armenian architecture had formed.