Robur
Robur Ammianus Marcellinus (30.3) mentions a fortress named Robur, which Valentinian I., A.D. 374, built near Basilia (Basle) on the Rhine in Switzerland. Schoepflin guessed that Robur was on the site of the cathedral of Basle, but the words of Ammianus do not give much support to this conjecture: Prope Basiliam, quod appellant accolae Robur.
Others have made other guesses.
From William Smith (ed.), Dictionary of Greek and Roman Geography. Text provided under a CC BY-SA license by Perseus Digital Library, http://www.perseus.tufts.edu, with funding from the National Endowment for the Humanities and Tufts University. Data accessed from https://github.com/PerseusDL/canonical-pdlrefwk/ on 17 October 2026.