Some have conjectured that Columbus was able to persuade the Catholic Monarchs of Castile and Aragon to support his planned voyage only because they were aware of some recent earlier voyage across the Atlantic. Some suggest that Columbus himself visited Canada or Greenland before 1492, because according to Bartolomé de las Casas he wrote he had sailed 100 leagues past an island he called Thule in 1477. Whether Columbus actually did this and what island he visited, if any, is uncertain. Columbus is thought to have visited Bristol in 1476. Bristol was also the port from which John Cabot sailed in 1497, crewed mostly by Bristol sailors. In a letter of late 1497 or early 1498, the English merchant John Day wrote to Columbus about Cabot's discoveries, saying that land found by Cabot was "discovered in the past by the men from Bristol who found 'Brasil' as your lordship knows". There may be records of expeditions from Bristol to find the "isle of Brazil" in 1480 and 1481. Trade between Bristol and Iceland is well documented from the mid-15th century.