These early riding traditions, which were strongly tied to the ruling caste of nobility (as only those of noble birth or caste could become cavalry warriors), now spread throughout the Eurasian steppes and Iranian plateau from around 600 BC and onwards due to contact with the Median Empire's vast expanse across Central Asia, which was the native homeland of the early, north-eastern Iranian ethnic groups such as the Massagetae, Scythians, Sakas, and Dahae. The successive Persian Empires that followed the Medes after their downfall in 550 BC took these already long-standing military tactics and horse-breeding traditions and infused their centuries of experience and veterancy from conflicts against the Greek city-states, Babylonians, Assyrians, Scythians, and North Arabian tribes with the significant role cavalry played not only in warfare but everyday life to form a military reliant almost entirely upon armored horses for battle.