The Cadusii (Ancient Greek: Καδούσιοι) were an ancient people living in north-western Iran.
The Cadusii lived in Cadusia – a mountainous district of Media Atropatene on the south-west shores of the Caspian Sea, between the parallels of 39° and 37° North latitude. This district was probably bounded on the North by the river Cyrus (today Kura, in the former Soviet Republic of Azerbaijan, historically known as Arran and Caucasian Albania), and on the South by the river Mardus (today Sefid River), and corresponds with the modern Iranian provinces of Gilan and Ardabil.
They are described by Strabo as a warlike tribe of mountaineers, fighting chiefly on foot, and well skilled in the use of the short spear or javelin. It is possible that the name of the Gelae (Gilites) – a tribe who are constantly associated with the Cadusii, to the point of considering the former the national name for the Cadusii – has been preserved in the modern Gilan.
No mention of the Cadusii has been found in Caucasian or Middle Eastern sources, and they are known only through Greek and Latin sources.
They appear to have been constantly at war with their neighbours. First subjected by the Assyrians, if we believe to Diodorus' doubtful sources, they were then brought in at least nominal subjection to the Medes, until they rebelled at the time of the king of the Medes Artaeus. In Ctesias' tale (reported by Diodorus) the war originated from an offence the king gave to an able powerful Persian, called Parsodes. After the offence Parsodes retired himself in the Cadusii's land with a small force and he attached himself with the most powerful of the local lords by offering his sister in marriage to him. At this point the country, who was subject to at least a nominal subjugation to the Medes, rebelled and chose as its war-leader Parsodes, giving him command of their army. Against these the Medes armed no less than eight hundred thousand men (these are the numbers given by Ctesias, which shouldn't be given much trust). Artaeus failed miserably in his attempt to reconquer the Cadusii and Parsodes was triumphantly elected king by the winners. Parsodes waged continuous raids in Media for all his long kingdom, and so did those who succeeded him, generating a state of perpetual enmity and warfare between Cadusii and Medes that continued until the fall of the Medes in 559 BC. But it must be remembered that all Greek records on the East before Cyrus must be treated with the utmost skepticism. This said, it may be that behind this legend there is a part of truth if we believe some scholars who identify Artaeus with Herodotus' Deioces, or better Duyakku, an important Mede chief in the age of Assyrian hegemony. Another point of interest in this story is that Ctesias here mentions for the first time the Cadusii. What seems more certain (in the report of Nicolaus of Damascus) is that near to the end of the Mede kingdom the Cadusii played an important role in bringing its downfall by allying themselves with the Medes' enemies, the [[Achaemenid Empire/]Persians]].