Sistān (سیستان), also known as Sakastān (سَكاستان "the land of the Saka") and Sijistan, is a historical and geographical region in present-day south-eastern Iran, south-western Afghanistan and north-western Pakistan. Largely desert, the region is bisected by the Helmand River, the largest river in Afghanistan, which empties into the Hamun Lake that forms part of the border between Iran and Afghanistan. Sistan derives its name from Sakastan ("the land of the Saka"). The Sakas were a Scythian tribe which migrated to the Iranian Plateau and Indus valley between the 2nd century BC and the 1st century, where they carved a kingdom known as the Indo-Scythian Kingdom. In the Bundahishn, a Zoroastrian scripture written in Pahlavi, the province is called "Seyansih". After the Arab conquest of Iran, the province became known as Sijistan/Sistan. The previous Old Persian name of the region, prior to Saka dominance, was zaranka ("waterland"). The older form is also the root of the name Zaranj, capital of the Afghan Nimruz Province. In the Shahnameh, Sistan is also referred to as Zabulistan, after the region in the eastern part of present-day Afghanistan. In Ferdowsi's epic, Zabulistan is in turn described to be the homeland of the mythological hero Rostam. In prehistoric times, the Jiroft Civilization covered parts of Sistan and Kerman Province (possibly as early as the 3rd millennium BC). It is best known from excavations of the archaeological site of Shahr-i Sokhta, a massive third millennium BC city. Other smaller sites have been identified in the region in surveys by American archaeologists Walter Fairservis and George Dales. The site of Nad-i Ali in Afghan Sistan has also been claimed to date from the Bronze Age (Benseval and Francfort 1994). Earlier the area was occupied by Iranian peoples related to the Aryans, Eventually a kingdom known as Arachosia was formed, parts of which were ruled by the Medean Empire by 600 BC. The Medes were overthrown by the Achaemenid Persian Empire in 550 BC, and the rest Arachosia was soon annexed.