I think there are 2 separate issues
a. From when do the Christian remains in Thessalonika (The Rotunda) date?
b. How do we define "early Christian" for the purposes of our "connection ?
Re the Thessalonikan remainsWiki is the only source I have found which suggests that conversion of the church was "by" Constantine. Whereas several other sources indicate a later conversion e.g
a.
Thessalonika Guide "converted into a Church during the reign of Theodosius the Great "
http://www.travel-thessaloniki.gr/destination_guide#_684225614b.
Journals of Early Christian Studies - Late 4th/Early 5th
http://muse.jhu.edu/login?uri=/journals/journal_of_early_christian_studies/v013/13.4n asrallah.pdfc.
Architecture of Alexandria and Egypt c300BC to AD700 - "converted ... in the 5th Century"
http://books.google.co.uk/books?id=KFNCaZEZKYAC&pg=PA351&lpg=PA351&dq=Thessaloniki+Ro tunda+Church+of+Hagios+Georgios&source=bl&ots=7ww3XrtG2s&sig=cGWls9MO425e38BUdEjpBkuk ft0&hl=en&ei=uyd3Su-hAeDKjAexmOSnBg&sa=X&oi=book_res The other issue is from when the remains inside the original Rotunda date -again the quotations seem to indicate that what remains are Byzantine mosaics from 6th Century. so, on both counts the Christian aspects of the site are post-Nicean.
re The Definition of "Early Christianity"When I suggested the Connection I took the definition from Wiki!! It seemed to have nice factual start and end dates viz Death of Christ c 30 AD/Council of Nicea 325AD. UNESCO on the other hand seems to like using the phrase "Paleo-Christian". Are they interchangeable then? Definitions of PaleoChristian which i have found include
a.
OED etc just say "related to early Christianity" which isn't much help!
b.
Britannica - "Early Christian art , also called Paleo-Christian art or primitive Christian art (is) architecture, painting, and sculpture from the beginnings of Christianity until about the early 6th century, particularly the art of Italy and the western Mediterranean. (Early Christian art in the eastern part of the Roman Empire is usually considered to be part of Byzantine art.)". Which is somewhat muddling as we already have "Byzantine" as a "connection"!!
I think my preference would be to stick with "Early Christian" as the title and the "Council of Nicea" as the end point - The Tarraco cemetary remains from the 3rd century are still pre Nicean even though they are described in this case as Paleochristian.
An alternative would be to alter the definition to include anything called "paleochristian" by UNESCO - but then we have to "solve" the issue of the "Byzantine overlap" for sites in the East!! And also what do we do with sites whose "era" is not described by UNESCO?