Ancient urban theatres are not known in Amiens, Beauvais, Noyon, Senlis. But two amphitheatres are known in Amiens and another in Senlis. Analysis of structures and of the plans of the rural theatres : similitaries and differences. Hollow structure : most often, light buildings with circular outer walls on foundations which still exist. The inner structure likely consisted of a wooden structure : pillars supporting floors and stepped rows of seats. Massive structure : at Ribemont-sur-Ancre (Somme) and Vendeuil-Caply (Oise), the theatre walls were made of massive masonry containing the inner banks of earth and chalk. The stone seating layon this bank or on massive vaulted masonry as in the amphitheatre in Amiens (Somme).