Abbatiale Saint-Pierre-et-Saint-Paul, Medieval abbey church in La Porte-du-Der, France.

The Abbatiale Saint-Pierre-et-Saint-Paul in La Porte-du-Der is built of light beige and grey stone blocks. Its rounded eastern end carries tall pointed windows with dark glass, with a ring of smaller arched windows above, and a steep dark grey conical roof topped by a small cross. A slender tower with a grey spire, louvered openings and a clock rises on the left, and a lower brown-roofed section extends to the right. The pre-Romanesque nave is among the oldest in France, and the choir is one of the few examples of Champenois Gothic alongside Laon and Noyon.

The foundation goes back to the 7th century when Saint Berchaire founded it, with the church receiving official consecration later in 998. In the 12th century the building underwent major rebuilding that decisively shaped its present appearance.

The church is still the parish church of Montier-en-Der, known locally as Saint-Rémy after the patron saint whose feast the inhabitants kept celebrating there once their own Saint-Rémy church was destroyed during the Revolution. The name Montier-en-Der comes from the Latin Monasterium Dervense given to Berchaire's monastery.

The church stands in the centre of Montier-en-Der, in the commune of La Porte-du-Der, between the Voire and the Magnentin. The former abbey buildings were razed in 1860; the national stud farm founded in 1806 occupies the site and its rebuilt buildings are listed as monuments historiques. The nave is the oldest part to look at first, then the choir of around 1200.

The nave stands as one of France's oldest examples of pre-Romanesque building and shows the shift between Carolingian and Romanesque architecture. This architectural feature makes it especially noteworthy for specialists and history-minded visitors.