The oldest known separate individual map of the island of Ireland has come to light in a 600-year-old atlas which is expected to sell for more than €3 million at auction in London next month.

Christie's auctioneers said the extraordinary 15th century map – "aptly bordered in bright green" – was the oldest known separate, individual map of the island.

The map is the first depiction of Ireland alone rather than together with Britain.

It is appearing for the first time at auction.

The map is hand-drawn on vellum (tanned sheepskin) and contained in an atlas made in Venice by renowned Italian navigator and cartographer Grazioso Benincasa in 1468.

The maritime atlas, of a type known to scholars as a “portolan”, contains seven double-page navigational maps designed for ships used in trade and exploration.

The map was made 24 years before Columbus discovered America, when Ireland was at the edge of the known western world.

Christie's maps expert Julian Wilson said travel to Ireland in the 15th century was "the equivalent of space exploration".

He said the atlas had probably been a prestigious commission intended for a wealthy owner to consult in the comfort of his home rather than for a sea captain to use on the high seas.

Mr Wilson said the "highly important and intriguing map" was inscribed "Irlanda que Ibernia dicitur" (Ireland which is called Hibernia).

Place names

He said 57 place names are identified, among them Porto Rosso (Portrush), Limerich, Chorca, Drogda (Drogheda); and Bre (Bray). The capital is not identified although a settlement spelt as Donvelim might, according to Mr Wilson, refer to Dublin or Dún Laoghaire.

Some offshore islands, including the Aran Islands and those in Clew Bay, are depicted in red, blue, green and gold.

Only two rivers feature in the map – what appear to be the Barrow and the Nore.

Other maps in the atlas show west Africa, the Canary Islands, France, Spain, Portugal and Britain.

Christie’s said the “extraordinarily rare” atlas was still in its original Venetian goatskin binding and “the colours and gilding remain as fresh and vibrant as the day it was finished”.

The atlas has been assigned a top estimate of £2.5 million (€3.2 million) for auction in London on November 19th.