Roman emperor Trajan invaded Dacia (Romania) because this kingdom threatened Rome's provinces south of the Danube River.  He was successful but the Dacians soon rebelled against Rome's military presence.  They are again defeated and Dacia is made into a Roman province.  Later in the quarter-century, the Parthians expelled the Roman appointed ruler of Armenia and put a friendly king on the throne.  Because of this, Trajan of Rome is inspired to conquer Armenia and Mesopotamia.  When he continued on to Babylon, these newly conquered territories rebelled and the Parthians invaded.  At this time, the Jews of Cyrenaica (in Libya) also rebelled against Roman and Greek oppression.  The revolt spread amongst Jews in other parts of Africa and the Middle East.  Trajan returned to Armenia and Mesopotamia, fought the Parthians and reconquered the provinces.  He also sent ruthless governors to quell the Jewish revolts in the other parts of the Roman empire.  Trajan died before being able to campaign into Mesopotamia again as he planned.   In 122, Hadrian started building a wall from the Tyne River to the Solway Firth to keep the Scottish Picts out of Roman Britain.

Notable Battles
102 Sarmizegethusa between Trajan and Decebalus.