The church of Saint Benoît, once the cathedral of Castres, and the most important of the churches of Castres today, dates only from the 17th and 18th centuries. The city hall occupies the former bishop's palace, designed in the 17th century by Jules Hardouin-Mansart (the architect of Versailles), and with gardens designed by André Le Nôtre (the designer of the gardens in Versailles). The Romanesque tower beside it ("Tour Saint Benoît") is the only survival of the old Benedictine abbey. The town possesses some old mansions from the 16th and 17th century, including the "Hôtel de Nayrac", of the Renaissance.