Navigation at sea is dangerous. Portolans are used to transmit the knowledge of the seafarers. These charts provide some major advantage over enemy ships and are considered as highly strategic.
The portolan is not a map in the modern geographic meaning. It is a document that sets islands and coasts and identifies the ports. The sailors are guided by the lines of the compass rose from focal points mostly in sixteen wind directions.
On November 19 in London, Christie's sells a manuscript on vellum of a portolan atlas of the coasts of Atlantic and North Sea, consisting of seven double-page charts 39 x 50 cm in a Venetian binding of the period, lot 45 estimated £ 1.5M.
The visit is progressive, from Sierra Leone to Jutland. It includes the discoveries made in the coast of Africa by Cadamosto, a Venetian serving the Portuguese, and by Pedro de Sintra in 1460.
One page is signed, located and dated : Gratiosus Benincasa Anchonitani, Venice, 1468. The Benincasa portolan anticipates by thirteen years the first Portuguese mission of African circumnavigation. He was one of the best cartographers of his time and his work in the Mediterranea are among the sources used to compile the Cornaro atlas in Venice around 1489.