Assumption of Mary Church, Koper, Romanesque cathedral in Koper, Slovenia.

The Cathedral of the Assumption of the Blessed Virgin Mary is a three-nave Romanesque basilica from the second half of the 12th century, of which only the south wall with walled-up Romanesque windows survives. Its east side on Titov trg is formed by the church and a four-storey Italian-style bell tower. The exterior has a Venetian Gothic ground floor from after the 1460 earthquake and a pure Renaissance upper storey; statues in the niches keep their own canopies.

The present church was built in the second half of the 12th century as a three-nave Romanesque basilica, of which only the south wall with blocked Romanesque windows survives. In 1380 the Genoese plundered Koper, burned the church and its atrium, and took the relics of Saints Nazarius and Alexander; rebuilding lasted over a century and the church was extended westward. After the 1460 earthquake the facade was redesigned in 1488 with Venetian Gothic and Renaissance elements.

Venetian artists contributed paintings to this cathedral, including a notable work by Vittore Carpaccio from the early 16th century. The collection reflects Italian artistic traditions that shaped this coastal settlement.

The cathedral stands on Titov trg, with its bell tower forming the eastern side of the square. The tower is four stories high and follows the Italian campanile style; it can be viewed from the square. The church is regularly open to visitors when services are not in progress.

One of Slovenia's oldest bells from 1333 hangs in the tower, predating many of the architectural changes that shaped this building. The bell serves as a testament to the site's long history of religious use.