In modern German, Saarbrücken literally means Saar bridges, and indeed there are about a dozen bridges across the Saar river. However the name actually predates the oldest bridge in the historic center of Saarbrücken, the Alte Brücke, by at least 500 years.
The name Saar stems from the Celtic word sara (streaming water), and the Roman name of the river, saravus.
However, there are three theories about the origin of the second part of the name Saarbrücken.
The most popular theory states that the historical name of the town, Sarabrucca, derived from the Celtic word briga (hill, or rock, big stone), which became Brocken (can mean rock or boulder) in High German. The castle of Sarabrucca was located on a large rock by the name of Saarbrocken overlooking the river Saar.
A minority opinion holds that the historical name of the town, Sarabrucca, derived from the Old High German word Brucca(German), meaning bridge - or more precisely a Corduroy road, which was also used in fords. Next to the castle, there was a ford allowing to cross the Saar.
A mostly rejected theory claims that the historical name of the town, Sarabrucca, derived from the Germanic word bruco (swamp, marsh). There is an area in St Johann called Bruchwiese (wiese meaning meadow), which used to be swampy prior to development, and there were flood-meadows along the river, and those are often marshy. However, the Saarbrücken area was first settled by Celts and not by Germanic peoples