The Parsis are the Zoroastrians of India, descended from those who left Iran after the Arab conquest, and their communal identity rests on a migration narrative that is also their principal historical problem.
The story is told in the Qissa-i Sanjan. A group of Zoroastrians sails from Iran, lands in Gujarat, and is granted asylum by a local ruler on conditions, that they explain their religion, adopt the local language, that their women wear the local dress, that weddings be held after dark, and that they lay down their arms. The best-known episode has the ruler send a vessel of milk filled to the brim, meaning that the land is full, and the Zoroastrian priest stir sugar into it without spilling any, meaning that his people will sweeten it without displacing anyone.
It is a very good story, and it was composed at least six hundred years after the events it describes. Its historical reliability is genuinely disputed among scholars, and the landing is dated variously to 716, 765 or 936. This atlas treats it as origin-legend rather than as chronicle, which is the standard scholarly position and not a fringe one.
What is solid is the outcome. A Zoroastrian community established itself in Gujarat, kept its priesthood, its fire temples and its purity law, adopted Gujarati and much local custom, and later moved in large numbers to Bombay under British rule, where it became prosperous out of all proportion to its size.
The conditions attached to the grant of asylum, whatever their historicity, describe accurately what the community in fact did: it explained itself, took the local language, and gave up the option of being anything other than a guest.