The Fortified Sector of Colmar (Secteur Fortifié de Colmar) was the French military organization that in 1940 controlled the section of the French frontier with Germany in the vicinity of Colmar. The fortifications were built as part of France's Maginot Line defensive strategy, but the sector lacks the large interconnected fortifications found along France's land border with Germany. The sector's principal defense was the Rhine itself, which could be crossed only by boat or by seizing a bridge crossing. The sector's fortifications chiefly took the form of casemates and blockhouses. The SF Colmar was flanked to the north by the Fortified Sector of the Lower Rhine to the north and the Fortified Sector of Mulhouse to the south. The Colmar sector was directly attacked by German forces on 15 June 1940, capturing or destroying most of the fortifications in the sector in three days.