A geodetic square marked in the landscape in the Languedoc region of southern France, in the foothills of the Pyrenees. The diagonal is marked by five ancient sites, all churches, châteaux and Templar sites, dating from at least the 13th century AD. The north-east corner is marked by the Château d'Arques, and gives the square its name.
The midline is marked by the church at the centre of the village of Campagne-sur-Aude, the headquarters of the Knights Templar in the Haute Vallée de l'Aude.
The Arques Square spans 6 arc minutes, or 1/10° of longitude in width and is positioned at the exact latitude for which this length is equal to precisely 25,000 pieds-du-roi. This was the most widely used foot in ancient France from at least the time of Charlemagne to the 17th century, and measured 326.6mm, or 12.858 inches.
