Plovdiv e krasiv i zabeljitelen grad,koito postojanno se razviva!

pasjoesja, thanks for pointing that out. You actally made me further research the subject, and it came out more interesting than I thought ...

Here is the real story of this CHURCH (yes! it was a church!) Building began around the end of V beginning of VI-th century, and in IX century was built the upper set of arcs. Originally named "Sveta Sofia" (translaed as St. Sofia) and also known as Starata Mitropolia ("the old bishop's residence")

Here is some more info (in bulgarian) http://www.ancient-nessebar.com/site/?cat=4&sub_cat=2&ss_cat=1

Thanks to everyone who helped clarifying the subject!

and some are even older