I was once told that the Roman emperor Constantine was the "father of church buildings."  It was said that, prior to his introduction of countless pagan features into Christianity, the early church met in houses, & fellowshiped & worshiped God as a casual group, not funneled through a pastor or worse, a priest.

Constantine was born about 285 AD.  This church dates from approximately 230 AD.  It's just one of many.  Notice that the architecture is nearly identical to a Catholic or Orthodox church of more recent times - the apse at the back of the sanctuary; the rectangular, forward facing nave; the mosaic on the floor; the whole congregation + priest facing the altar together.

But that's not new.  This is - a cave was discovered below it.  Archaeologists have found that this cave is where Christians worshiped before the legalization of Christianity meant they would no longer be thrown to the lions.  They believe it may date from 33-70AD.  Among lamps, a cemetery, a cistern, and a dwelling, they found stone seats, an apse, and an inscription of the "70 beloved by God".  Some great photos are here.

It's clear that after living and worshiping literally underground (in the catacombs of Rome and caves like this) for centuries, when allowed to worship freely, early Christians did what they always intended to do - build edifices to lift the mind & heart to Heaven and to bring glory to God. 

Previously, the oldest known church edifices found have been from the 200's.