The basilica of Catechumens is located in the northwest corner of the city below the castle of Servia and it was the church of the Bishop. It is dated around 1000, but it was exposed to modifications in several periods from the 12th to the 16th century.

The church is a three-aisled timber-roofed basilica with narthex. The central aisle is elevated with windows. The aisles are separated by walls with with arched openings.The central aisle communicated with the sode ones through a ''trivilon''. The monument preserves mural decoration which is dated in three periods. The first wall paintings are contemporary with the initial phase of the church, the second layer is dated in the 13th century,when Michael was a bishop, while the last one, whose fragments were discovered during recent excavations, can be dated in the 15th-16th century. The fragments of mural paintings that were found in the south aisle, which was used as a chapel in the early post-Byzantine period, have particular interest. The fragments of three figures - Christ Pantocrator, a praying one and St. Dimitrios- may consist the scene of a Deisis. These fragments, along with other details such as stones of the floor in the two side aisles and the wall paintings of the third period, which are preserved in the north and south aisle, confirm that the basilica was at least in use on the side aisles until the 16th to 17th century.

Nowadays,the ruins of the basilica are preserved. During the years 1995-2000 excavations and rescue interventions were carried out in the masonry and the wall paintings because they were necessary for the study of the restoration of the monument. Those revealed valuable information about the history of the monument.