There were many so-called secret voyages to the New World in not so ancient times. Maps were secret documents of royalty. They were treasure maps; new lands being potential sources of wealth. Only captains of officially sponsored voyages, were privy to them. Cover stories of specific destinations were common tactics.
Gunnar Thompson is favorite writer of mine because, in keeping with my research, he is correct in his historical reconstructions. He has done extensive and detailed studies tracing the origin of New World cultures to India and Asia. I recommend his book, Nu Sun, about Asian – American Voyages in 500 BC. Thompson is an artist and has carefully reproduced the art of Asian cultures and the same with New World cultures and placed them side by side. There can be do doubt that the latter had their origin in Asia.
In another book, Secret Voyages to the New World, he unveils some most interesting revelations about these secret voyages. The facts in this book, or his other works, won’t soon be in school textbooks. It upsets too many long held beliefs.
I don’t think my friend Fred Jueneman will object to my use of his brief review of this book, recently posted on the internet.
According to Gunnar Thompson (Secret Voyages to the New World, Misty Isles Press, Seattle, 2006), Marco Polo's voyages under the aegis of Kublai Khan were over a century prior to Gavin Menzies' 1421: The Year China Discovered America, outlining the armadas of Zheng He during the reign of Emperor Zhu Di.
Thompson daringly has Marco Polo on two voyages to the west coasts of the Americas to oversee the marketing strategies of Kublai Khan's vast overseas interests. (The Polo brothers and Marco weren't the only Europeans in China at this time, as Genoese and Venetian commercial enterprises competed fiercely for such trade.) More recently, as an historical detective, Thompson has uncovered a collection of maps and letters from Marco Polo's daughters, some of which had lain fallow at the Library of Congress when they were archived there by the Rossi family in the 1930s. Moreover, Thompson also speculates that the north magnetic pole was in the vicinity of the Arctic Circle as early as the 13th century, as later European explorers who used magnetic compasses (in defiance of canon law) thought they were sailing north when their voyages were actually more westerly, since they were surprised at the temperate climates and grape vines found in their New World landings.
Satellite positioning and more earthbound measurements have indeed found a radical northward migration of the north magnetic pole, from the Canadian archipelago and now heading into Russian waters. The USGS had been constantly upgrading their maps because of this known magnetic migration. Whether or not this migration is solar caused is as yet not known for certain.