One of the perennial pre-Columbian contact theories involves ancient visits by the Chinese to America. This is made plausible for several reasons. First of all, the voyage around the great circle route across the Pacific is facilitated by almost constant visibility of land and prevailing sea-currents. China had advanced maritime technology long before the European age of discovery, and historically were known to have taken long sea voyages to distant ports such as Africa, Arabia and India before Vasco de Gamma set sail. And lastly, there are suggestive Chinese accounts of lands far to the East in their chronicles.