The twelfth Duke of Edinburgh Lecture was presented in London on 15 October 1986 at the Royal Geographical Society to the thirty-ninth Annual General Meeting of the Institute, the President in the Chair. The lecturer, the President said in his introductory remarks, was a geographical scholar who had devoted much of his time to the verification of early voyages by following the paths described in the often legendary accounts:the travels of Marco Polo in 1961 and later the voyages on which the present paper is based, of St Brendan, Sindbad and Jason. In 1976–7 in the medieval leather boat Brendan he followed a route from Ireland across the Atlantic described in the 8/9th century Navigatio. In 1980–81 in the Arabian boom Sohar he sailed over 6000 miles from Oman to Canton in a reconstruction of Sindbad's seven voyages described in One Thousand and One Nights, and finally in 1984 in Argo, a reconstructed Greek vessel of the 13th century B.C., his voyage took him from Greece through the Bosphorus to Georgia in the USSR, following the legendary path of Jason in search of the Golden Fleece. No-one could be better fitted to reflect on the human factor in early navigation.