Flevum

Flevum was a Roman castrum and naval base in Frisia, identified with modern Velsen in the Netherlands, controlling the Oer-IJ, the northernmost outlet of the Rhine. Flevum I was built around 14-16 AD to support Germanicus's campaigns after the Teutoburg Forest disaster, later expanding from 1 to 2 hectares with a river port, four jetties, and ship sheds. After its likely destruction during the Frisian revolt of 28 AD, Flevum II was established circa 40 AD under Caligula. Archaeologists recovered 520 lead slingshots from the site, evidence of a fierce attack, along with imported Mediterranean goods and human remains in the harbor.