Roman Emperor Trajan transformed the borough of the Serdi into a city which he called Ulpia Serdica.

Gallienus established a mint at Sardica, and Constantine the Great, who was born in the region, contemplated making it his capital.

Again occupied by the 'Greek' Byzantines from 1018 to 1186, it enjoyed great prosperity; a section of the population was Paulician or Manichaean, heresies from both Catholic and (later) Orthodox points of view.

In 1382 the city was captured by the Ottoman Turks, and for more than four centuries it was the residence of the beglerbeg (governor general) of all Rumelia.

Emperors Constans and Constantius, the two remaining sons of Constantine worked together at the urging of Pope Julius in response to this heresy that not only divided the church, but the state as well.

In addition to the attempt to resolve the Arian issue, other major points were: An Apostolic vicariate (missionary pre-diocesan jurisdiction, entitled to a titular bishop) was created here at an early date and confided to the Franciscans.

It was suppressed towards the end of the eighteenth century, because the Catholics felt persecuted by the Turks and had emigrated, mostly to imperial Austria-Hungary and Russia, yet in 1758 restored, now as Apostolic Vicariate of Sofia–Plovdiv .

Relative peace was restored in 1835, and Rome confided the direction of the Catholics to the Redemptorists, under a vicar Apostolic who had not received episcopal consecration.

; all Latin Rite) Apostolic Vicars of Sofia–Plovdiv The position of a Titular Bishop of Philippopolis (in Thracia) (i.e. Plovdiv) existed since 1893 and 1967[4] It was originally just called Philippopolis, until 'in Thracia' was added (distinguishing it from several homonymous sees) in 1926 (in curiate Italian; also in Latin in 1933).