Originally its communal organization, Mons was a City Hall called "House of Peace." Earlier the deputy mayors were on the castle of the Counts of Hainaut, and now it is only the conciergerier, Saint-Calixte chapel and some underground rooms and the chamber. This place is now Castle Park, where we can also see the belfry. Already in the 13th century, the counts mentioned the House of Peace, located in Nimy Street. Other documents of the same time let one suppose that there existed two Houses of Peace, the one in Nimy Street and the other in the market area.