The church of Saint-Hermeland, of great architectural quality, is one of the first buildings classified as historical monuments in France, since 1862. Its sculpted decorations are among the richest and most varied of the Parisian suburbs. It was built between 1160 and 1230, at a time of great renewal of religious architecture, since the Gothic style, which is said to have been invented at the Abbey Church of Saint-Denis in 1140, will allow thanks to technical advances (vault on ogive cross, flying buttress) to pierce the walls and bring light into the churches, thus supplanting Romanesque architecture in Île-de-France and then throughout the country.
Although smaller in size, it is compared to the Notre-Dame Cathedral in Paris, on which the parish of Bagneux depended. Almost contemporary, geographically close, they have stylistic similarities that may suggest that the Notre-Dame workers worked at Bagneux. It contains raised funerary slabs dating from the 13th to the 16th centuries, a 17th century organ stand.