Deportation is the forced expulsion of individuals or groups by a state, though its precise definition varies—often overlapping with "expulsion" or "removal"—and it is strictly prohibited in its collective form under international law. Historically, it dates back to antiquity, with the Neo-Assyrian and Neo-Babylonian empires deporting the Israelites and Judeans in the 8th and 6th centuries BC (e.g., after the fall of Judah in 597 BC). The Achaemenid Empire used it as a punishment for rebels, while the Parthian Empire saw rare instances, such as the 10,000 Roman POWs from the Battle of Carrhae (53 BC) being resettled near Merv. The Sasanian Empire practiced it on a grand scale during Roman wars, deporting Emperor Valerian after the Battle of Edessa and founding cities like Gundeshapur with captives, which inadvertently spread Christianity. Today, a deportee is anyone under sentence of deportation, and the distinction between legal and illegal immigrant removal further complicates the term's modern usage.