"This limestone church is made up of a 13th century Laon Gothic choir, a late 15th century Hainaut Gothic nave, extended by two chapels, Gothic to the north and Baroque to the south, and a Baroque tower from the first half of the 18th century.
The choir is the oldest part of the church. Dated to the 13th century by archaeologists, it is with some vestiges of the medieval enclosure, the oldest chimacian monument.
Its general appearance presents the characteristics of the primitive Gothic style of the Soissonnais and the Laonnois. Its flat chevet is made up of three narrow, lanceolate, third-point windows with common uprights, surmounted by a rose window. Its walls made of freestone and seated limestone rubble are assisted by buttresses.
The original south chapel was erected at the same time as the choir. Transformed over the centuries, it currently has two parts: the chapel of the Blessed Sacrament and a space reserved for the sacristy.
The Gothic chapel, on the north side, completed in 1501, included the old Sainte Catherine chapel dating from the 14th century and served in the 16th century as a place of burial for the prestigious Croÿ family. Today it is dedicated to Saint Nicholas.
The vessel is in the “late” Hainaut Gothic style (15th century). Indeed, the architectural decor, both exterior and interior, combines simplicity with sobriety. The absence of decoration on the capitals of the columns is the best proof of this.
High tripartite windows under a pointed arch and molded tracery illuminate the naves and side aisles with soft natural light.
The absence of flying buttresses, the interior buttresses, the single saddleback under the naves, whose vaults are located almost at the same height, make the collegiate church similar to the many "hall" type churches that have flourished throughout Europe, from 13th century to 16th century.
Before briefly evoking the interior, it is necessary to underline an original feature of the Chimacian church: it was simultaneously parochial and collegiate until the end of the Ancien Régime.
Indeed, at the beginning of the 12th century, a chapter of secular canons was founded by the local lord Alard. These clerics, constituted as a college, quickly incorporated the parish church with its income. However, the two clergy cohabited, not without certain clashes: the vessel was the parish part, the choir, the almost exclusively canonical space."