A rare Portuguese manuscript titled 'Instrument of Possession' has been discovered by researcher Yashodhan Joshi in Lisbon, shedding light on the formal transfer of Bombay from Portuguese control to the British Crown on February 18, 1665. This 10-page document details the negotiations and conditions surrounding the transfer, which was part of a marriage treaty between King Charles II of England and the Portuguese princess Catherine of Braganza. The manuscript highlights the strategic consolidation of Bombay’s islands, previously a collection of fishing villages, into a unified territory. It also reflects the anxieties of the Portuguese regarding the rising influence of Chhatrapati Shivaji Maharaj, indicating that European powers viewed his ascent as a significant threat. Additionally, the document outlines conditions ensuring the rights of Portuguese subjects and their access to the harbor. Joshi's findings underscore the political complexities of the time and provide valuable insights into the historical context of Bombay's evolution into a major colonial port city. The manuscript serves as a crucial primary source for understanding the intersection of geography, trade, and politics in shaping modern Mumbai.