THE 'UBIER MONUMENT'

The so-called Ubier Monument, the 'Monument of the Ubii' (the local Germanic tribe) was discovered in 1965 when a house was built on the site. It is preserved to a height of 6 m and marks the southeast corner of the later Roman colony. Remains of the late 1st century city wall are still attached to the structure, which is almost a century older. Originally, the monument was at least 12 m high. Its foundations were set in the former flood plain of the Rhine, 6 m lower than street level in Roman times. Stability was ensured by ramming a grid of oak piles into the underlying gravel to bear a cement-like base made of greywacke and lime mortar (opus caementitium). On this was erected the tower made of large tuff blocks. Analysis of the wood in the pile grid allowed the structure to be dated to AD 4/5. When the city wall was built at the end of the 1st century, part of the tower was demolished and the rest integrated in the new wall. The original purpose of the structure is debated. It was probably part of an earlier fortification of the Oppidum Ubiorum at the entrance to the Rhine harbour.