"Seres" was given to northwestern China by traders who approached it through the highlands of central Asia from Samarcand, while "Sinae" was the name given to southeastern China by traders who approached it by way of the Indian ocean, and heard of it in India, but never reached it. Apparently no European ships ever reached China before the Portuguese, in 1517.[313] The name "Sinae" or "Thin" seems to mean the country of the "Tchin" dynasty, which ruled over the whole of China in the second century before Christ, and over a portion of it for a much longer time. The name "Seres," on the other hand, was always associated with the trade in silks, and was known to the Romans in the time of the Emperor Claudius,[314] and somewhat earlier. The Romans in Virgil's time set a high value upon silk, and every scrap of it they had came from China. They knew nothing about the silk-worm, and supposed that the fibres or threads of this beautiful stuff grew upon trees. Of actual intercourse between the Roman and Chinese empires there was no more than is implied in this current of trade, passing through many hands. But that each knew, in a vague way, of the existence of the other, there is no doubt.[315] [Footnote 310: Diodorus Siculus, i. 70.] [Footnote 311: Strabo, xi. 7, Sec. 3.] [Footnote 312: Robertson, _Historical Disquisition concerning the Knowledge which the Ancients had of India_, Dublin, 1791, p. 55. I never have occasion to consult Dr. Robertson without being impressed anew with his scientific habit of thought and the solidity of his scholarship; and in none of his works are these qualities better illustrated than in this noble essay.] [Footnote 313: The Polos sailed back from China to the Persian gulf in 1292-94; see below, p. 282.] [Footnote 314: The name "Seres" appears on the map of Pomponius Mela (cir. A. D. 50), while "Sinae" does not. See below, p. 304. Jam Tartessiaco quos solverat aequore Titan In noctem diffusus equos, jungebat Eois Littoribus, primique novo Phaethonte retecti Seres lanigeris repetebant vellera lucis. Silius Italicus, lib. vi. _ad init._] [Footnote 315: For this whole subject see Colonel Sir Henry Yule's _Cathay and the Way Thither_, London, 1866, 2 vols.,--a work of profound learning and more delightful than a novel.] [Sidenote: Cosmas Indicopleustes.] [Sidenote: Shape of the earth, according to Cosmas.]