Gilbert became one of the leading advocates for the then-mythical Northwest Passage to Cathay (China), a country written up in great detail by Marco Polo in the 13th century for its abundance of riches. Gilbert made an elaborate case to counter the calls for a Northeast Passage to China. During the winter of 1566 he and his principal antagonist Anthony Jenkinson (who had sailed to Russia and crossed that country down to the Caspian Sea) argued the pivotal question of polar routes before Queen Elizabeth. Gilbert claimed that any north-east passage was far too dangerous: ""the air is so darkened with continual mists and fogs so near the pole that no man can well see either to guide his ship or direct his course."" By logic and reason a north-west passage was assumed to exist, and Columbus had discovered America with far less evidence; it was imperative for England to catch up, to settle in new lands and thus to challenge the Iberian powers. Gilbert's contentions won support and money was raised, chiefly by the London merchant Michael Lok, for an expedition. The fearless Martin Frobisher was appointed captain and left England in June 1576, but the quest for a north-west passage failed: Frobisher returned with a cargo of a black stone – which was found to be worthless – and a native Inuit.