Before crossing to Asia, Alexander wanted to safeguard his northern borders. In the spring of 335 BC, he advanced to suppress several revolts. Starting from Amphipolis, he travelled east into the country of the "Independent Thracians"; and at Mount Haemus, the Macedonian army attacked and defeated the Thracian forces manning the heights. The Macedonians marched into the country of the Triballi, and defeated their army near the Lyginus river (a tributary of the Danube). Alexander then marched for three days to the Danube, encountering the Getae tribe on the opposite shore. Crossing the river at night, he surprised them and forced their army to retreat after the first cavalry skirmish.