The Bras de Bronne, a tributary of the Canche that crosses the city, once served as a natural border. While part of the village was in Artois, the bell tower was in Boulogne: the parish came under the diocese of Boulogne. The patron saint is the founder of the neighboring diocese, Firmin, first bishop of Amiens. In the choir is a beautiful effigy of the saint, sculpted in the 16th century. Marles-Sur-Canche and its parish church dedicated to Saint Firmin contain treasures such as the statue of Saint Nicolas from the 16th century, the bronze bells from 1805 or the Altar from the 18th century. Despite its humble appearance, its history is set in stone. The building combines a sober nave with a beautiful choir in Flamboyant Gothic style, more slender. This contrast between the two sides is astonishing. The Saint Firmin church is thus strongly marked by the architectural heritage of the 15th century. The Marlois are attached to their church which, despite regular work since 1812 and the numerous renovations, shows a worrying state of health, visible by the numerous deteriorations: cracks, detachment of the cladding, broken stones, crumbling, weakened masonry of the buttresses, decaying structural wood.