It seems clear, however, that the main purpose of Alexander was to attack and humble the Triballi. Their locality is known generally as the region where the modern Servia joins Bulgaria. They reached eastward (in the times of Thucydides, ii. 96) as far as the river Oskius or Isker, which crosses the chain of Hæmus from south to north, passes by the modern city of Sophia, and falls into the Danube. Now Alexander, in order to conduct his army from the eastern bank of the river Nestus, near its mouth, to the country of the Triballi, would naturally pass through Philippopolis, which city appears to have been founded by his father Philip, and therefore probably had a regular road of communication to the maritime regions. (See Stephanus Byz. v. Φιλιππόπολις.) Alexander would cross Mount Hæmus, then, somewhere north-west of Philippopolis. We read in the year 376 B. C. (Diodor. xv. 36) of an invasion of Abdêra by the Triballi; which shows that there was a road, not unfit for an army, from their territory to the eastern side of the mouth of the river Nestus, where Abdêra was situated. This was the road which Alexander is likely to have followed. But he must probably have made a considerable circuit to the eastward; for the route which Paul Lucas describes himself as having taken direct from Philippopolis to Drama, can hardly have been fit for an army. The river Lyginus may perhaps be the modern Isker, but this is not certain. The Island called Peukê is still more perplexing. Strabo speaks of it as if it were near the mouth of the Danube (vii. p. 301-305). But it seems impossible that either the range of the Triballi, or the march of Alexander, can have extended so far eastward. Since Strabo (as well as Arrian) copied Alexander’s march from Ptolemy, whose authority is very good, we are compelled to suppose that there was a second island called Peukê higher up the river. The Geography of Thrace is so little known, that we cannot wonder at our inability to identify these places. We are acquainted, and that but imperfectly, with the two high roads, both starting from Byzantium or Constantinople. 1. The one (called the King’s Road, from having been in part the march of Xerxes in his invasion of Greece, Livy, xxxix. 27; Herodot. vii. 115) crossing the Hebrus and the Nestus, touching the northern coast of the Ægean Sea at Neapolis, a little south of Philippi, then crossing the Strymon at Amphipolis, and stretching through Pella across Inner Macedonia and Illyria to Dyrrachium (the Via Egnatia). 2. The other, taking a more northerly course, passing along the upper valley of the Hebrus from Adrianople to Philippopolis, then through Sardicia (Sophia) and Naissus (Nisch), to the Danube near Belgrade; being the high road now followed from Constantinople to Belgrade.