Sea in culture of barbarian invaders and knowledge of geography took a backward step. In the seventh century, Isidore of Seville produced a "wheel map" in which Asia, Africa and Europe were arranged like segments in an orange, separated by the "Mare Mediterranean", "Nilus" and "Tanais" and surrounded by "Oceanus". It was not until the fifteenth century that Ptolemy's maps were used again and Henry the Navigator of Portugal initiated ocean exploration and maritime research. Encouraged by him, Portuguese navigators explored, mapped and charted the west coast of Africa and the Eastern Atlantic and this knowledge prepared the way for the great voyages
Gulls of Europe, Asia and North America had previously collaborated on two other volumes in the Helm series, on terns and skuas. The following is a list of errors in the corrected reprint: Gulls of Europe, Asia and North America Gulls of Europe, Asia and North America by Klaus Malling Olsen and Hans Larsson is a volume in the "Helm Identification Guides" series of bird identification books. The book is intended to succeed Peter J. Grant's "" as the standard identification work on Northern Hemisphere gulls. Although the Helm series already contained a volume on seabirds, by Peter Harrison, gulls compete for space in that volume with