The castle was constructed in the 1220s by Enguerrand III de Coucy. The castle proper occupies the tip of a bluff or falaise. It forms an irregular trapezoid of 92 x 35 x 50 x 80 m. At the four corners are cylindrical towers 20 m in diameter (originally 40 m in height). Between two towers on the line of approach was the massive donjon (keep). The donjon was the largest in Europe, measuring 35 meters wide and 55 meters tall. The smaller towers surrounding the court were as big as the donjons being built at that time by the French monarchy. The rest of the bluff is covered by the lower court of the castle, and the small town.