Of the Romanesque basilica from the 13th century, the nave and the square of the choir are preserved. In the 15th century, when the side aisles were removed and the arcades were bricked up, the basilica changed into a hall church. In addition, entrance halls were added on the north and south sides in more recent times. The church was once surrounded by a six- to seven-meter high defensive wall from the first half of the 16th century in the form of an irregular quadrilateral with towers in each corner. Parts of the west side of the wall were already demolished around 1800 to build a town hall. A century later, the remains of the western defense wall and the southwest tower were also taken down to build a school building. The northeast tower and the gate were also demolished, leaving only the southeast tower. The north-we
st tower, which was converted into a keep, later collapsed; between 1848 and 1858 it was replaced by a bell tower. The bell from 1570 is a donation of the mayor of Mauritius Ludwigs from Rupea. Two wooden sculptures from pre-Reformation times have been preserved in Mercheasa: a Madonna with remarkable drapery from the first half of the 15th century and a large crucifix from the transition period from Gothic to Renaissance. The organ was erected in 1788 by Johannes Prause and in 1887 W. Hörbinger expanded it to ten stops.
