THE HUMAN SPECIES. 443 



equally anxious to prevent them penetrating to the 

 south, since they also had raised a great wall, or conti- 

 nuous lines of defence, from Bactria to the Caspian, a 

 rampart like the Kizil Alan, most likely older than 

 the accession of the Sassanian dynasty ; since further 

 west, the wall between the two seas, passing from 

 Derbend (Porta portarum, Portas Caspiae) to the 

 Euxine, appears also to be more ancient than his- 

 torical record. 



The Yuei-chi, the last Caucasian race that left the 

 north central high land of Asia, being pressed by the 

 Mongolians, or by Huns from the north-east (about 

 200 B. C.), were compelled to quit Chensi, and fell 

 upon the Sai, or Sakas, who, retreating, divided into 

 two great masses, whereof the first directed its course 

 towards the west, and the other, not quite so nume- 

 rous, fell back upon Southern Thibet, and thence came 

 down upon the Greek Bactrian state (B. C. 90), then 

 ruled by Mithridates. They had, at the same time, 

 similar conflicts with the Parthians, whose king, Ar- 

 taban, they slew. They gave an asylum to Sanotrokes, 

 and restored him to power (B. C. 76). From Bactria 

 they crossed the Paropamissus, and subdued another 

 Greek sovereignty in Afghanistan, on the south side 

 of the chain. Passing onwards, they formed a pro- 

 vince of Scinde ; but, in an attempt to penetrate further 

 eastward, they were routed by Vikra-maditya, king of 

 Avanti (B. C. 56). If not from an earlier invasion, it 

 was, at the latest, in consequence of this defeat, that 



