Inter caetera ('Among other [works]') was a papal bull issued by Pope Alexander VI on the 4 May 1493, which granted to the Catholic Monarchs King Ferdinand II of Aragon and Queen Isabella I 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 whether the pope intended a "donation" of sovereignty or an infeudation 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. Inter caetera and its supplement Dudum siquidem (September 1493) are two of the Bulls of Donation. While these bulls purported to settle disputes between Spain and Portugal, they did not address the exploratory and colonial ambitions of other nations, which became more of an issue after the Protestant Reformation. Background Before Christopher Columbus received support for his voyage from Queen Isabella and King Ferdinand of Spain, he had first approached King John II of Portugal. The king's scholars and navigators reviewed Columbus's documentation, determined that his calculations grossly underestimated the diameter of the Earth and thus the length of the voyage, and recommended against subsidizing the expedition. Upon Columbus's return from his first voyage to the Americas, his first landing was made in the Portuguese Azores; a subsequent storm drove his ship to Lisbon on 4 March 1493. Hearing of Columbus's discoveries, the Portuguese king informed him that he believed the voyage to be in violation of the 1479 Treaty of Alcáçovas. The treaty had been ratified with the 1481 papal bull Aeterni regis, which confirmed previous bulls of 1452 (Dum diversas), 1455 (Romanus Pontifex), and 1456 (Inter caetera), recognizing Portuguese territorial claims along the West African coast. It was the King's understanding that the terms of the treaty acknowledged Portuguese claims to all territory south of the Canary Islands (which had been ceded to Spain). Columbus's arrival in supposedly Asiatic lands in the western Atlantic Ocean in 1492 threatened the unstable relations between Portugal and Spain. With word that King John was preparing a fleet to sail to the west, the King and Queen of Spain