The church of Saint-Martin, a wide church with a transept, has one of the tallest bell towers of the fortified churches in the Thiérache, but probably also the slimmest. At ground level, the interior measures only three by three metres. It is so slender that it was not possible to install a staircase. Thus, the inhabitants of Laigny had to use an outside ladder to reach the escape room on the upper floor in case of an attack.

The ornamentation of black glazed bricks dates from the time when the building was fortified, probably in 1673 together with the sacristy, which is, incidentally, the oldest in the Thiérache.

The tower and transept have the same sandstone base as the nave, with the superstructure of the transept and choir made of brick, as is the upper part of the tower. The only recognisable defensive elements are traces of embrasures in the tower.

An idea of the original church can be seen on the north wall of the nave, where four large walled arcades are still visible, probably left over from a former side aisle. The new windows installed there, however, are not very nice to look at.

When we visited, it was locked, and there is no evidence of a key either.