The Saka or Saca (Persian: old Sakā, mod. ساکا; Sanskrit: Śaka; Greek: Σάκαι, Sákai; Latin: Sacae; Chinese: , old *Sək, mod. Sāi) was the term used in Persian and Sanskrit sources for the Scythians, a large group of Eastern Iranian nomadic tribes on the Eurasian Steppe. Modern scholars usually use the term Saka to refer to Iranians of the Eastern Steppe and the Tarim Basin.René Grousset wrote that they formed a particular branch of the "Scytho-Sarmatian family" originating from nomadic Iranian peoples of the northwestern steppe in Eurasia. They migrated into Sogdiana and Bactria in Central Asia and then to the northwest of the Indian subcontinent where they were known as the Indo-Scythians. In the Tarim Basin and Taklamakan desert region of Northwest China, they settled in Khotan and Kashgar which were at various times vassals to greater powers, such as the Han and Tang dynasties of Imperial China.