Columbus returned in March 1493 and by May the Castilian crown had a papal grant. Inter Caetera, dated 4 May 1493, gives Ferdinand and Isabella and their successors all islands and mainlands found and to be found, discovered and to be discovered, lying west and south of a line drawn from pole to pole one hundred leagues west of the Azores and Cape Verde, provided those lands were not already held by a Christian prince. The stated purpose is missionary. The grant is made so that the peoples living there may be instructed in the Catholic faith and in good morals, and the monarchs are charged to send men fit for that work.
Alexander VI was a Valencian, elected with Spanish support, and the speed and generosity of the grant were noticed at the time. Portugal, which held the older bulls and a fleet in the South Atlantic, refused the line outright. Rather than appeal to Rome the two crowns negotiated directly, and in the Treaty of Tordesillas of 7 June 1494 they moved the boundary to three hundred and seventy leagues west of Cape Verde, a shift that later placed Brazil on the Portuguese side.
So the bull's own line lasted thirteen months and was superseded by a treaty between the parties it was meant to separate. What lasted was the premise underneath it: that lands occupied by people who were not Christian could be granted away by a third party who had never seen them.