Marcianopolis, or Marcianople was an ancient Roman city in Thracia. It was located at the site of modern day Devnya, Bulgaria.

The city was so renamed by Emperor Trajan after his sister Ulpia Marciana, and was previously known as Parthenopolis. Romans repulsed a Gothic attack to this town in 267 (or 268), during the reign of Gallienus. Diocletian made it the capital of the Moesia Secunda province.

Valens made it his winter quarters in 368 and succeeding years, Emperor Justinian I restored and fortified it. In 587, it was sacked by the king of the Avars but at once retaken by the Romans. The Roman army quartered there in 596 before crossing the Danube to assault the Avars.

Between 893 and 972 it was one of the most important medieval cities in south-eastern Europe.