Around 513 BC, as part of the military incursions ordered by Darius I, a huge Achaemenid army invaded the Balkans and tried to defeat the Western Scythians roaming to the north of the Danube river.[8] Several Thracian peoples, and nearly all of the other European regions bordering the Black Sea (including parts of the modern-day Bulgaria, Romania, Ukraine, and Russia), were conquered by the Achaemenid army before it returned to Asia Minor.[4][8] Darius's highly regarded commander Megabazus was responsible to fulfill the conquers in the Balkans.[8] The Achaemenid troops conquered Thrace, the coastal Greek cities, and the Paeonians.[8][9][10] Eventually, in about 512-511 BC, the Macedonian king Amyntas I accepted the Achaemenid domination and surrendered his country as a vassal state to the Achaemenid Persia.[8][11] The multi-ethnic Achaemenid army possessed many soldiers from the Balkans. Moreover, many of the Macedonian and Persian elite intermarried. For instance, Megabazus' own son, Bubares, married Amyntas' daughter, Gygaea; and that supposedly ensured good relations between the Macedonian and Achaemenid rulers.[8]