No more interesting ethnographical inquiry could be found in relation to the people of India than how these races, having got thus far on their way, ever succeeded in getting to the south of the peninsula. It could only have been the earliest arrivals on the frontier who passed on. Later arrivals from Western Persia (amongst whom we may reckon the Medes or Meds) remained in the Indus valley. The bar to frontier progress lies in the desert which stretches east of the Indus from the coast to the land of the five rivers. This is indeed India's second line of defence, and it covers a large extent of her frontier. Conquerors of the lower Indus valley have been obliged to follow up the Indus to the Punjab before striking eastwards for the great cities of the plains. Thus it is not only the Indus, but the desert behind it, which has barred the progress of immigration and conquest from time immemorial, and it is this, combined with the command given by the sea, which differentiates these southern gates of India from the northern, which lead on by open roads to Lahore, Delhi, and the heart of India. The answer to the problem of immigration is probably simple. There was a time when the great rivers of India did not follow their courses as they do now. This was most recently the case as regards the Indus and the rivers of Central India. In the days when there was no Indus delta and the Indus emptied itself into the great sandy depression of the Rann of Katch, another great lost river from the north-east, the Saraswati, fed the Indus, and between them the desert area was immensely reduced if it did not altogether disappear. Then, possibly, could the cairn-erecting stone-monument building Dravidian sneak his way along the west coast within sight of the sea, and there indeed has he left his monuments behind him. Otherwise the Dravidian element of Central Southern India could only have been gathered from beyond the seas; a proposition which it is difficult to believe. However, never since that desert strip was formed which now flanks the Indus to the east can there have been a right-of-way to the heart of India by the gateways of the west. The earliest exploration of these western roads, of which we can trace any distinct record, was once again due to the enterprise of the Greeks. We need not follow Alexander's victorious footsteps through India, nor concern ourselves with the voyage of his fleet down the Indus, and from the mouth of the Indus to Karachi. General Haig, in his pamphlet on the Indus delta, has traced out his route[3] with patient care, demonstrating from observations taken during the course of his surveys the probable position of the coast-line in those early days.