India sat at the centre of the ancient world's trade network for at least four thousand years. Marco Polo travelled to China overland in 1271 and came home by sea in 1295, dispatched by Kublai with a Yuan princess to the Persian Ilkhan, Fujian to Persia by ship and then Black Sea to Venice. Sea travel was, and is, safer, and it carries far more. He was one of perhaps hundreds of European merchants who ever made that journey, against the thousands of Arabs, Persians, Indians and Southeast Asians who used the Indian Ocean routes as a matter of routine. The Silk Road of popular imagination, a highway from Chang'an to the Mediterranean, was in reality a scatter of local overland links, and the volumes it carried were dwarfed by what moved by sea, where Indian merchants and Indian gold held the centre of the network. Mesopotamia is conventionally called the cradle of civilisation. Its ancient economy rested on sheep-farming and woollen cloth, traded for Anatolian metal and shipped eastward for what resident Indian merchants and artisans, well documented in the Mesopotamian record, were bringing in. Meanwhile the Indus-Saraswati sites keep getting older. Bhirrana is now dated to before 7,000 BC, and the submerged material off the Gulf of Khambhat, and more recently off Poompuhar in Tamil Nadu, points to port cities that predate almost everything currently taught as the beginning. The Khambhat evidence rests on dredged rather than in-situ material and remains contested; the Poompuhar and Dwarka surveys are ongoing. The maritime story has been missing from the standard history. It is finally being addressed, especially around the Indian coast, and there is still much to do. My full conversation with @rschoudhary108 below.

India Converted Half of Asia Without an Army. One of the largest cultural expansions in history was carried out almost entirely by merchants waiting for the monsoon wind to change. Over roughly a thousand years India gave much of Asia its religions, its epics, its scripts and its ideas of kingship, using convoys timed to the monsoon's twice-yearly reversal rather than armies. Buddhism set aside caste and the food laws that made travel among strangers difficult, and it moved east in the holds of merchant ships until, by one count, China had thirty thousand monasteries and close to two million monks. The courts of Southeast Asia adopted Sanskrit, Indian law and Indian statecraft by choice, judging it the best system on offer to a king who wanted to look legitimate at home and abroad. The former Thai capital Ayutthaya took its name from Ayodhya, the city of Rama. Angkor Wat, the largest religious monument on earth, is a working diagram of the Indian cosmos, its moat standing for the ocean that surrounds Mount Meru. The era's other great power took a different route. China's Confucian order required a foreign ruler to acknowledge the emperor as his superior before exchange could happen, tribute, not trade. The ports of the region answered to Chinese demand while its temples, script and kingship were Indian-influenced. It wasn't wholly peaceful. The Indianised kingdoms fought each other readily enough. What the pattern lacked, for the better part of a thousand years, was an Indian conqueror. I've written up the full story, with sources and further reading. Link to essay in the comments below.

Pythagoras never claimed to have invented his theorem. Indian altar-builders had been using it in the Sulba Sutras a thousand years before he was born, to size fire altars for Vedic ritual. He was born on Samos to a Sidon-based merchant father and reportedly lived in India for several years, according to Apollonius of Tyana.