The Roman Castle can be visited
Roman Castle CAELIVS MONS (Caelius Mons)

Caelius Mons (German: Himmelsberg) was a late antique cohort fort of the Danube-Iller-Rhine Limes (DIR) in the province of Raetia secunda and is part of the Kellmünz Archaeological Park in Kellmünz an der Iller in the district of Neu-Ulm. The current municipal name Kellmünz could be traced back to "Caelius Mons".
The fort was located in the present-day western village center of Kellmünz and is almost completely built over. On the southeast corner of the complex is the Roman Catholic Church of St. Martin. The location was favored by a ridge that rises 35 m above the Iller (Hilaria) valley. On its eastern side, this is more easily accessible, which necessitated special fortification of this section.
The name is handed down in the Notitia dignitatum as Caelius after Caelius, one of the seven hills of Rome. The garrison of the fort is named as cohors III Herculea Pannoniorum.
The complex belongs to the late Roman Danube-Iller-Rhine Limes, a border fortification that was built around 300 AD after the fall of the Upper Germanic-Raetian Limes along these rivers. Compared to the forts of the middle and high imperial period, smaller complexes were built that exploited strategically favorable terrain situations. Very similar complexes of the Danube-Iller-Rhine Limes existed nearby, among others in Kempten (Cambodunum) on the Burghalde, Isny (Vemania fort) and Gundremmingen (Bürgle). Most of these complexes existed until the early 5th century AD.
In the Middle Ages, the fort was gradually demolished and the material used for castle and church construction.
Research History+
Already in the middle of the 19th century, Roman wall sections were discovered in Kellmünz. Systematic excavations of large parts of the stone defensive wall took place between 1901 and 1913 by the history-enthusiastic Kellmünz merchant Roman Lindner and his three sons. The autodidacts were advised by the archaeologist Paul Reinecke (1872–1958). During these investigations, a large number of partly high-quality spolia were recovered from the late antique masonry, including architectural parts of monumental buildings and large marble statues cut to size for installation. The sale of these spolia to the Bavarian National Museum in Munich financed the elaborate excavations in the first years.
Between 1986 and 1993, the University of Munich, under the direction of archaeologist Michael Mackensen, carried out extensive excavations again. Subsequently, the Kellmünz Archaeological Park was established, where the visibly preserved fort remains are accessible to the public.
Complex+
Terrain and Extent of Construction
The excavations provided evidence of a polygonal fort that was excellently protected by the terrain. The slopes on the west and southwest sides fall steeply to the Iller. On the north side, the plateau is separated by an erosion channel from two further spur-like rock outcrops. Only on the east side was approach easy. Here was the "front" of the camp with the only larger gate; at this point, the wall was up to 3 m thick. Due to the size of the camp, the unit could have been up to 300 men strong.
Only a short time before construction began, a small settlement of half-timbered construction was erected at the site of the later fort. A building cut during Mackensen's excavations had channel heating. Two freshly minted coins, found under the screed of this house, date its origin to no earlier than 297 AD. A pointed ditch, about 4.5 meters wide, was dug around this settlement, separating the plateau to the east. The excavators suspected that these settlement structures could have belonged to a construction camp. The construction of the fort itself began in the last years of the 3rd century.
Along the east side, a pointed ditch (5–6 m wide, 2.5 m deep) and a 6 m wide flat-bottomed ditch served as obstacles to approach. The walls with an opus caementitium core largely consisted of reused spolia in the lower section. They enclosed an inner area of 0.86 ha with a length of 101.50 m and a width of 98.50 m. Approximately 14 towers were embedded in the wall, mostly semicircular, projecting at the gate, and ¾-round at the corners of the east side. A tower with a rectangular ground plan on the west side is likely to have been built due to static problems with the eroded steep slope.
Source: Wikipedia · Licence: CC BY-SA 4.0
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 48.1201, 10.1268