Accounts of Megasthenis (Greek Ambassador to Chandragupta courts), mention Sandracottus (Chandragupta) as Alexander's contemporary.
Sir Jones mapped Sandracottus to Chandragupta Maurya. Thus:
Halt! There are two Chandragupta: Chandragupta Maurya and Chandragupta Gupta. It was Chandragupta Gupta who was the contemporary of Alexander.
So a correct timeline for Indian History is:
3138-1634 BCE Shishunga and earlier dynasties
1634-1534 BCE Nanda
1534-1319 BCE Maurya
1294 BCE Kanishka of Kushan Dynasty
327 BCE Chandragupta Gupta
57 BCE Vikramaditya Gupta
1887-1807 BCE Gautam Buddha Why?
1864-1792 BCE Mahaveer Jain Why?
509- 477 BCE Aadi Shankaracharya Why?
References:
Gautam Buddha
Mahavir Jain
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The Jaina tradition holds that Mahaveer left this world 15 years after the death of Bhagawan Buddha (1807 BCE), ie, in 1792 BCE, and since Mahaveer lived for a span of 72 years, he must have been born in 1864 BCE
Mahavir taught his philosophy during the reign of Ajatshatru ie. 1814-1787 BCE.
Shankara
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The date of Shankara, as per the current chronology, is 788-820 CE (derived from Shankara Digvijaya Sara) However, since the "sheet-anchor" is displaced backwards, it is apparent that the date of Shankara would be recalculated to be around 600 BCE.
Brihat Shankara Vijaya, gives a date of 509 BCE. Nepal Rajavamshavali states the date of 487 BCE.