 Describing the Battle of Marathon, during the Greek-Persian war (490 BC), the author noted that Udi soldiers also were at war as a part of nine satrapy of the Persian army.The Udis are mentioned in the "Geographica" of the ancient Greek writer Strabo (1st century BC) in his description of the Caspian Sea and the Caucasian Albania.The ethnic term "Udi" was mentioned first in the Natural history by the ancient Roman author Pliny the Elder (1st century AD).