Arengario is old Town Hall of Monza dating back to the thirteenth century. Built on the sidelines of Pratum magnum, historic market place, it is the most important civil building in the city, symbol of communal autonomy. The type of building, lower porch, refers directly to Palazzo della Ragione in Milan (1228): it is a brick building with overhanging two-tone decors lancet windows in neo-Romanesque style. The porch is characterized by pointed arches resting on 18 pillars seats on three rows of six. The porch were guarded units for Medieval measures used by traders (now placed at the entrance of Public Library). On the south facade, gable, is a stone loggia added in 1380, known in dialect as "Parléra", from which were read old decrees. In the middle of the thirteenth century it was added a bell tower with square plant, with two mullioned windows with pointed arches, Ghibellines battlements and octagonal spire with tip. The clock was built by Giovanni Dondi. Currently Arengario is an exhibition space.