Bactria was a Persian satrapy before Alexander's invasion but when he passed through it on his way to India he founded twelve cities and settled a considerable number of his soldiers in them. It formed part of the Empire of Seleucus but declared itself independent in 250 B.C. about the same time that the Parthians revolted and founded the Empire of the Arsacidae. The Bactrian kings bore Greek names and in 209 Antiochus III made peace with one of them called Euthydemus, in common cause against the nomads who threatened Western Asia. Demetrius, the son of this Euthydemus, appears to have conquered Kabul, the Panjab and Sind (c. 190 B.C.) but his reign was troubled by the rebellion of a certain Eukratides and it is probable that many small and contending frontier-states, of which we have a confused record, were ruled by the relatives of one or other of these two princes. The most important of them was Menander, apparently king of the Kabul valley. About 155 he made an incursion to the east, occupied Muttra and threatened Pataliputra itself but was repulsed. He is celebrated in Buddhist literature as the hero of the Questions of Milinda but his coins, though showing some Buddhist emblems, indicate that he was also a worshipper of Pallas. Shortly after this Hellenic influence in Bactria was overwhelmed by the invasion of the Yüeh-chih, though the Greek principalities in the Panjab may have lasted considerably longer. In the reign of Mithridates (c. 171-138 B.C.) the Parthian Empire was limitrophe with India and possibly his authority extended beyond the Indus. A little later the Parthian dependencies included two satrapies, Aracosia and the western Panjab with capitals at Kandahar and Taxila respectively. In the latter ruled kings or viceroys one of whom called Gondophores (c. 20 A.D.) is celebrated on account of his legendary connection with the Apostle Thomas. More important for the history of India were the conquests of the Sakas and Yüeh-chih, nomad tribes of Central Asia similar to the modern Turkomans[116]. The former are first heard of in the basin of the river Ili, and being dislodged by the advance of the Yüeh-chih moved southwards reaching northwestern India about 150 B.C. Here they founded many small principalities, the rulers of which appear to have admitted the suzerainty of the Parthians for some time and to have borne the title of satraps. It is clear that western India was parcelled out among foreign princes called Sakas, Yavanas, or Pallavas whose frontiers and mutual relations were constantly changing. The most important of these principalities was known as the Great Satrapy which included Surashṭra (Kathiawar) with adjacent parts of the mainland and lasted until about 395 A.D.