The Roman Empire at its greatest was during the rule of Trajan, from AD 98 to AD 117. Trajan conquered lands no Roman thought possible. He fought and won the Dacian Wars (102-106) and soon after defeated Britain (109). He defeated the Parthians at Ctesiphon in 116, and captured Armenia in 117. He pushed on toward Germany, but could not capture Teutoburg Forest. The Roman Empire now had all the lands from Mauritania in the south, to Britannia in the North, to Mesopotamia and Armenia in the East. In the year 117, Hadrian became the new Emperor. He built forts around the empire to defend against the "Barbarian" armies. The most famous was Hadrian's Wall in northern England. Still standing today, this wall was built to keep out the powerful Caledonian armies from the north.