The earliest recorded history of the region dates back to about 500 BC when much, if not all, of modern Tajikistan, was part of the Achaemenid Empire. Some authors have also suggested that in the 7th and 6th centuries BC, parts of modern Tajikistan, including territories in the Zeravshan valley, formed part of the ancient Hindu-practicing Kambojas tribe before it became part of the Achaemenid Empire.