GENERAL INTRODUCTION 7 



From the fourth century a.d. onwards, when civilization 

 suffered at the hands of barbarian invaders, know- 

 ledge of the geography of the world received a great set- 

 back. Fantastic suggestions were made as to the shape 

 of the world, and Isidore of Seville in the seventh century 

 originated the "wheel maps" in which the world was repre- 

 sented as being surrounded by a circle of water as was 

 thought in Homeric times (Fig. 2). In addition the world 



Fig. 2. — Wheel Map of Isidore of Seville. 



was cut up into three portions by waters connected with this 

 circle of ocean, an eastern portion, Asia, and two western 

 portions, Europe in the north and Africa in the south. 

 For many years little advance was made save for information 

 obtained by Norsemen in the north and voyages of the 

 Arabs in the east, and in the fifteenth century the maps 

 of Ptolemy reappeared. But the knowledge of the oceans 



