the meridian to the right was defined by inter caetera
, the one to the left by the treaty of tordesillas
. modern boundaries and cities are shown for purposes of illustration.
inter caetera ("among other [works]") was a papal bull issued by pope alexander vi on the fourth of may (quarto nonas maii) 1493, which granted to the catholic majesties of ferdinand and isabella (as sovereigns of castile) all lands to the "west and south" of a pole-to-pole line 100 leagues west and south of any of the islands of the azores or the cape verde islands.
it remains unclear to the present whether the pope was issuing a "donation" of sovereignty or a feudal infeodation or investiture. differing interpretations have been argued since the bull was issued, with some arguing that it was only meant to transform the possession and occupation of land into lawful sovereignty. others, including the spanish crown and the conquistadors, interpreted it in the widest possible sense, deducing that it gave spain full political sovereignty.
the inter caetera bull and others similar to it, particularly dudum siquidem, made up the bulls of donation.