Media was a political entity centered in Ecbatana that existed from the 7th century BCE until the mid-6th century BCE and is believed to have dominated a significant portion of the Iranian plateau, preceding the powerful Achaemenid Empire. The frequent interference of the Assyrians in the Zagros region led to the process of unifying the Median tribes. By 612 BCE, the Medes became strong enough to overthrow the declining Assyrian empire in alliance with the Babylonians. However, contemporary scholarship tends to be skeptical about the existence of a united Median kingdom or state, at least for most of the 7th century BCE.