It is very important to note that some 2,500 years ago at the least Pythagoras went from Samos to the Ganges to learn geometry...But he would certainly not have undertaken such a strange journey had the reputation of the Brahmins' science not been long established in Europe

Observing and studying in this way, Pythagoras traveled for many years. Some say he got as far as India and was deeply influenced, for he took up Oriental dress, including a turban. And certain of his mystical ideas, such as number magic and reincarnation, were typical of the Fast.

Some writers think that he did. Others accept that he studied and absorbed in some form the Vedic philosophy of ancient India; certainly it was known in Persia at this time. And there was probably direct contact between India and Greece before the time of Alexander. Vitsaxis G. Vassilis, in his book Plato and the Upanishads, argues that exponents of literature, science, philosophy and religion traveled regularly between the two countries. He points to accounts by Eusebius and Aristoxenes, of the visits of Indian sages to Athens and their meetings with Greek philosophers. And reference to the visit of Indians to Athens is found in the fragment of Aristotle preserved in the writings of Diogenes Laertius who was also one of Pytha-
goras' biographers.

Philostratus devoted two and a half of the eight books of his Life of Apollonius (1.19-3.58) to the description of a journey of his hero to India. According to Philostratus' Life, en route to the Far East, Apollonius reached Hierapolis Bambyce (Manbij) in Syria (not Nineveh, as some scholars believed), where he met Damis, a native of that city who became his lifelong companion. Pythagoras, whom the Neo-Pythagoreans regarded as an exemplary sage, was believed to have travelled to India. Hence such a feat made Apollonius look like a good Pythagorean who spared no pains in his efforts to discover the sources of oriental piety and wisdom. As some details in Philostratus’ account of the Indian adventure seem incompatible with known facts, modern scholars are inclined to dismiss the whole story as a fanciful fabrication, but not all of them rule out the possibility that the Tyanean actually did visit India.[18] On the other hand, there seemed to be independent evidence showing that Apollonius was known in India. In two Sanskrit texts quoted by Sanskritist Vidhushekhara Bhattacharya in 1943[19] he appears as "Apalūnya", in one of them together with Damis (called "Damīśa"). There it is claimed that Apollonius and Damis were Western yogis who held wrong Buddhist views, but later on were converted to the correct Advaita philosophy.[20] Classical philologists believed that these Indian sources derived their information from a Sanskrit translation of Philostratus’ work (which would have been a most uncommon and amazing occurrence), or even considered the possibility that it was really an independent confirmation of the historicity of the journey to India.[21] Only in 1995 were the passages in the Sanskrit texts proven to be interpolations by a modern (late 19th century) forger .[22]

The Ghaggar is an intermittent river in India, flowing during the monsoon rains. It originates in the Shivalik Hills of Himachal Pradesh and flows through Punjab and Haryana to Rajasthan; just southwest of Sirsa in Haryana and by the side of talwara jheel in Rajasthan, this seasonal river feeds two irrigation canals that extend into Rajasthan.

The present-day Sarsuti Saraswati River originates in a submontane region (Ambala district) and joins the Ghaggar near Shatrana in Punjab. Near Sadulgarh (Hanumangarh) the Naiwal channel, a dried out channel of the Sutlej, joins the Ghaggar. Near Suratgarh the Ghaggar is then joined by the dried up Drishadvati (Chautang) river.

The wide river bed (paleo-channel) of the Ghaggar river suggest that the river once flowed full of water, and that it formerly continued through the entire region, in the presently dry channel of the Hakra River, possibly emptying into the Rann of Kutch. It supposedly dried up due to the capture of its tributaries by the Indus and Yamuna rivers, and the loss of rainfall in much of its catchment area due to deforestation and overgrazing.[1] This is supposed by some to have happened at the latest in 1900 BCE, but is much earlier

* 2500 BC — Sahara becomes fully desiccated. Desiccation had been proceeding from 6000 BCE, as a result of the shift in the West African tropical monsoon belt southwards from the Sahel. Subsequent rates of evaporation in the region led to a drying of the Sahara, as shown by the drop in water levels in Lake Chad. Tehenu of the Sahara attempt to enter into Egypt, and there is evidence of a Nile drought in the pyramid of Unas.
* 2200 BC — Beginning of a severe centennial-scale drought in northern Africa, southwestern Asia and midcontinental North America, which very likely caused the collapse of the Old Kingdom in Egypt as well as the Akkadian Empire in Mesopotamia.