This is the oldest building in the city that has survived to this day. Built in the 4th century in the center of the residence of Emperor Constantine the Great, it is funny that it is still located in a huge “stone bag” whose walls make up the Office of the President of Bulgaria and various government institutions. The church is active, at least the schedule of services is written on the sign.

One of the oldest rotundas in the city from the era of Constantine the Great, when Christianity started to be accepted in the Roman empire. Small (as such churches used to be from that period), but very nice with atmosphere. There's a never leaving homeless lady sitting at the entrance :)

This is Sofia’s oldest church dating back to the 4th century with frescoes from the 8th century onwards. Some are in reasonable condition, others less so but given its age and history, it is worth a quick visit. Free to enter. No photos allowed. The church is built on the Roman foundations of the city which can be viewed in an extended area outside the church.

This is the oldest surviving building in town. Built in the 4th century as a Roman Bath, you can still see the ruins of the bath behind the church. The Church of Saint George is a late Antique red brick rotunda. Later it became a church inside the walls of Serdika. It was a mosque during Ottoman rule in 16th century and later a Bulgarian Orthodox Church.