Untere Gaisenbergbastion (Werk XXI)

Thick limestone walls rise out of the greenery at the southern end of Stuttgarter Straße. They are what remains of the Untere Gaisenbergbastion, Work 21 of the federal fortress that once ringed Ulm. The whole system ranked among the largest in Europe. Captain Vogt directed its construction between 1843 and 1858. It was a closed bastion, complete in itself, with ramparts on all four sides. Its task was to guard the eastern flank of the Michelsberg between Courtine 20 and Courtine 22.

In its day the work bristled with defences. A mortar battery stood at the left shoulder, and a Bonnet casemate crowned the salient. In front lay a dry moat and then a glacis, the open slope that left attackers exposed. A double caponnière ran along the right shoulder, a covered passage into the moat. The great defensive barracks stood in the gorge, and powder magazines hid inside the rampart. In wartime it held about 1,867 men, a small town under arms. Württemberg pioneers garrisoned it first, and from 1897 the 1st Battalion of Infantry Regiment 127 took over. Earth covered the salient battery in 1880, and in 1896 the reduit, the inner fort, gained a storey. After the First World War the reduit served as a dwelling.

Demolition for the university almost erased the bastion between 1960 and 1966. Parts of the front escarp, the Bonnet casemate and the right flank with its battery survived. The double caponnière now houses a student café and the carnival guild Ulmer Haglhex. The meeting place Charivari occupies that same flank. You can still find the escarp's arched top near the staff car park by the H building, barely clearing the soil. Shrubs crowd the stone, and their roots bite into the limestone, a lesson in why fortress walls need steady care.