While evidence of settlement at present-day Wiesbaden dates back to the Neolithic era, historical records document continuous occupancy after the erection of a Roman fort in 6 AD which housed an auxiliary cavalry unit. The thermal springs of Wiesbaden are first mentioned in Pliny the Elder's Naturalis Historia. They were famous for their recreation pools for Roman army horses and as the source of a mineral used for red hair dye (which was very fashionable around the turn of BC/AD among women in Rome).
The Roman settlement is first mentioned using the name Aquae Mattiacorum (Latin for "Waters of the Mattiaci") in 121. The Mattiaci were a Germanic tribe, possibly a branch of the neighboring Chatti, who lived in the vicinity at that time. The town also appears as Mattiacum in Ptolemy's Geographia (2.10). The line of Roman frontier fortifications, the Limes Germanicus, was constructed in the Taunus not far north of Wiesbaden.
The capital of the province of Germania Superior, Mogontiacum (present-day Mainz), base of 2 (at times 3) Roman legions, was just over the Rhine and connected by a bridge at the present-day borough of Mainz-Kastel (Roman "castellum"), a strongly fortified bridgehead.
The Alamanni, a coalition of Germanic tribes from beyond the Limes, captured the fort c. 260. Later, in the 370s, when the Romans and Alamanni were allied, the Alemanni gained control of the Wiesbaden area and were in charge of its defense against other Germanic tribes.
After the Franks under Clovis I defeated the Alamanni in the Battle of Tolbiac in 496, the Franks eventually displaced the Alamanni in the Wiesbaden area over the course of the 6th century. In the 8th century, Wiesbaden became the site of a royal palace of the Frankish kingdom. The first documented use of the name Wiesbaden is by Einhard, the biographer of Charlemagne, whose writings mention "Wisabada" sometime between 828 and 830.
When the Frankish Carolingian Empire broke up in 888,
