Calo: unidentified Roman fort, part of the Rhine limes.
Calo was a fort of a Roman cavalry squadron, halfway between Xanten and Moers-Asberg. Although the military settlement is mentioned in our sources, it is still unidentified. As the Rhine is a meandering river, it is very likely that the remains have been destroyed, but surprises can, of course, never be excluded.
The name Calo may be derived from *Kalona, which revers to grey stones near waterways (cf. Calonne near Calais).