The first settlements date from 1500 BC. Celtic tribe named Brigantii is mentioned by Strabo as a sub-tribe in these region of the Alps. In the 5th century BC, the Celts settled at Brigantion, which was one of their most heavily fortified locations. After battles in 15 BC, the Romans conquered Brigantion and the city became a Roman camp. It was conferred the status of a municipality (Brigantium) around 50 AD and was the seat of the Roman admiralty for Lake Constance. In 259/60 Brigantium was destroyed by the Alemanni, a Germanic people who settled in the area in around 450.
From 610 to 612 St. Columbanus and Saint Gall worked as missionaries in Bregenz. From 917 the castle served as a residence of the Udalrichinger (ruling dynasty of Vorarlberg), who called themselves Counts of Bregenz. The house died out around 1150. The son of the first Ulrich was Saint Gebhard, born in 947. He became Bishop of Konstanz and was later known as the patron of the pregnant women. In around 1170 Hugo of Tübingen (Montfort) founded a town settlement (first documented mention in 1249), enlarged in the 13th and 14th century and from 1650 to 1652.
The city was sold in 1451 and in 1523 to the Habsburgs and continued under Austrian rule, with a brief occupation by Swedish forces under Carl Gustaf Wrangel during the 30 Years' War, until the 19th century. Bregenz was under Bavarian rule from 1805 to 1814. From 1842 to 1850, the harbour on Lake Constance was built. In 1883 and from 1889–1891 the harbour was enlarged, and Austrian ship service was set up in 1884. Rail communication has existed since 1872 and since 1884 across the Arlberg massif. Since then, the town has extended to the surrounding countryside. Since 1726, Bregenz has been the main seat of Austrian administration in Vorarlberg (Obervogtei, in 1786 Kreisamt, since 1861 seat of the Landtag, since 1918 seat of the Landeshauptmann). Rieden-Vorkloster and Fluh were incorporated into Bregenz in 1919 and in 1946,
