In the course of the Roman Alpine campaign of 16/15 BC, the Lake Constance region was integrated into the Roman Empire. During the campaign, there was also supposed to have been a battle on Lake Constance. The geographer, Pomponius Mela, makes the first mention in 43 AD of Lake Constance as two lakes – the "Lacus Venetus" (Upper Lake) and the "Lacus Acronius" (Untersee) – with the Rhine flowing through both. Pliny the Elder referred to Lake Constance as "Lacus Brigantinus" for the first time. The most important Roman site was Bregenz, which soon became subject to Roman municipal law and later became the seat of the Prefect of the Lake Constance fleet. The Romans were also in Lindau, but settled only on the hills around Lindau as the lakeshore was swampy. Other Roman towns were "Constantia" (Constance) and "Arbor Felix" (Arbon).