SaarbrÃ 1\/4 cken has 180,000 inhabitants and is on the river Saar .
Historic landmarks in the city include the stone bridge across the Saar ( 1546 ) , the Gothic church of St Arnual , the 18th century SaarbrÃ 1\/4 cker Schloss ( castle ) and the old part of the town , the St. Johanner Markt . In 1815 SaarbrÃ 1\/4 cken came under Prussian control , and for two periods in the 20th century ( 1919 â `` 35 and 1945 â `` 57 ) it became part of the Saar territory under French administration .