The Varbola Stronghold (Latin: Castrum Warbole, Estonian: Varbola Jaanilinn) was the largest circular rampart fortress and trading centre built in Estonia, in Harju County (Latin: Harria) in the 10th – 12th centuries. Parts of the ruins of the 580 metre long and 8-10 metre high limestone wall of the fortress stand until this day. The long gateways with multiple gates were built to defend the entrances. In these sections higher defensive towers were erected. There was a 13 metre deep well in the middle of the fortress and the territory held about 90 structures with furnaces for accommodation built with limestone floors and foundations.