In Roman times the Via Raetia passed through the area of the modern town. The first documentary mention of the village "Diezen" dates from 1039, the name meaning waterfall. From 1050 on a local nobility is mentioned, the family of the
Counts of Dießen-Andechs. The counts had their castle on the south of the town on the Schatzberg and in the years between 1121 and 1127, they founded the Dießen monastery. Around 1140 the family moved to
Wolfratshausen and left the town to the monastery though they still acted as bailiffs. With the extinction of the Counts of Andechs in 1248, the
Wittelsbacher took over the bailiwick of the monastery. Already in 1251 the place appears as the market town of Diessen. In the course of the war between
Ludwig the Bavarian and
Frederick the Fair Dießen was burned in 1318 and 1320 by the troops of Duke Leopold. After the victorious
battle of Mühldorf Ludwig raised the place to Bannmarkt. This meant that until
secularisation in 1803, there were two strictly separate legal areas in the area of today's township, the ducal and later electoral Bannmarkt Dießen and the Klosterhofmark Dießen-St. Georgen. The market Dießen itself was under the control of ducal, later electoral judges, who also held jurisdiction over the Ammersee and since 1599 also over the forested area west of the town called Forst Bayerdießen. This market judge office even held the blood or
high jurisdiction. In the
Thirty Years' War the town was plundered by Swedish troops in 1632 and most of its inhabitants fled either to Erlaich island in the lake or the extensive forests around town. In the
War of the Spanish Succession Dießen was again looted in 1703 by Austrian troops, the population fled again to Erlaich island in the lake. Already in 1704 it came to further raids by hussars. In the years 1743 and 1744 it came again to a cast by Austrian troops. The monastery church, the
Marienmünster, was rebuilt in the years 1732 to 1739 by the Baroque master builder
Johann Michael Fischer. The monastery was dissolved in 1803 in the course of secularization and parts of the monastery were demolished and most of its land sold off. With the start of steam shipping on the lake and the railroad service from Augsburg to Weilheim towards the end of the 19th century, Dießen became a center of attraction for artists and a center of the arts and crafts movement. From the 1920s onwards the town expanded in all directions with new settlement and building areas. == Dießen Abbey ==