In the Roman Era, the Lahn presumably was used by the Romans to supply their fort at Bad Ems, Kastell Ems. Here the "Limes Germanicus" on the borders of Germania Superior and Rhaetia crossed the Lahn. Archaeological finds are known from Niederlahnstein, as well as from Lahnau. One Lahnau site, the Waldgirmes Forum in the community of Waldgirmes, was discovered in the 1990s and had been the site of a Roman town. Another site in the community of Dorlar has the remains of a Roman marching camp (or "castra"). These Lahnau sites have significant altered the current understanding of the history of the Romans east of the Rhine and north of the "Limes".