The carreira da India and the problem of the access to the Tagus river rill: navigation obstacles during the sixteenth and seventeenth centuries

In late sixteenth century, due to fortification works, the navigation channels of the Tagus river rill began to silt, to narrow and to present a smaller depth, strongly affecting the shipping, especially carreira da India's ships, themselves characterized by its large dimensions. The largest concern was the carreira de Sao Giao (Sao Juliao), the northern navigation channel, and the most important one for vessels on their way to Lisbon, which became more susceptible of being the stage of beaching and shipwrecks. This study aims to contribute to the discussion of these subjects, while attempting, at the same time, to understand when the carreira de Alcacova, in the South channel, started being used by navigation to enter the Tagus river, and under which conditions.