This is a big church in Romano-Gothic style, built in the 13th century, although the closure of the choir dates from the 15th century. The big, massive looking tower is as wide as the single-aisled nave. On top is a saddle-roof, as is common for churches from this period. Originally the tower stood free from the church, the connecting part between them dates from the 19th century. The tower itself is probably younger than the church and must have been built ca. 1300.
The walls of the nave and transept are divided in two zones; the lower zone is decorated with pointed blind niches, with a few gates in between, which often are bricked up. In the upper zone are pointed windows. The gables of the transept have more blind niches, of which those on the north side are filled with decorative brickwork in different patterns. Traces of two demolished apses at the southern transept-arm are visible. Most of the church is covered by mellon-vaults, a typical feature of Romano-Gothicism.
The choir originally had a straight closure, which no doubt was as decorated as the other walls. In the 15th century the current Gothic closure replaced it. The entire choir is covered by a Gothic star-vault. This part of the church now serves as a mausoleum for Adriaan Clant, who signed the peacy treaty of Munster in 1648 as the representative of Groningen and surroundings. The tomb dates from 1672 and was made by Rombout Verhulst, one of the major sculptors of his time.
In the corner between the choir and the northern transept-arm is a sacristy from the 16th century of which only the outer walls survived a restoration in 1877-1878. It was this restoration that determined much of the church's current look. Before that the protestants had mutilated much of the church, enlarging windows and plastering the vaults. In 1828 and 1836 enormous buttresses had been built to support the tower.
It was the news about a planned further mutilation of the interior that urged P.J.H. Cuypers, in his function as a member of the national counsil of advisors for monuments, to take action. He managed to convince a majority of the members of the church-counsil of the need for a more historically correct restoration, which would be paid for by the government. Extremist elements in the protestant community however protested, claiming that a restoration lead by a catholic would be a first step towards a new catholic use of the church. In the end however most people were satisfied. The restoration, according to plans by Cuypers and executed by his assistant J.J. van Langelaar, resulted in a reconstruction of windows and niches on the outside as well as the repainting of the murals on the vaults. The tower and nave were connected by a new section. Of the sacristy only the walls remain, the interior was completely renewed. Cuypers' restoration in medieval style and the use of cement and paint to simulate stone caused a controversy within the national counsil of advisors, which as a result was disbanded by the minister in 1879.
A second restoration followed in 1937-1939 by architects Wittop and Koning. This time the buttresses of the tower were removed. The section between tower and nave was lowered and given a seperate roof. The interior was partly spoiled by the use of modern cement to plaster the vaults.