CLASSICAL AND EARLY MEDIEVAL HERITAGE 19 



attempted to extend two parallels eastwards on the basis of 

 the relative directions between important places noted by 

 travellers and also on the assumption that districts with 

 similar climates and products would lie on or near the same 

 parallel. In this way he established two main parallels, one 

 running along the assumed axis of the Mediterranean (Gibral- 

 tar-Messina-Rhodes) continued through the Taurus, the 

 Caspian Gates and along the Imaus mountains. For another he 

 assumed that Meroe in Egypt lay on the same parallel as south 

 India. 



The establishment of meridians, for reasons already 

 stated, presented still greater difficulties. Without the aid of 

 the magnetic compass, it was extremely difficult to determine 

 the bearing of one place from another. This knowledge was 

 derived from approximate astronomical observations, such as 

 the position of sunrise at the equinoxes, or of the constellations 

 in the night sky. From these Eratosthenes established an initial 

 meridian, which assumed that the mouth of the Don, Lysi- 

 machia on the Dardanelles, Rhodes, Alexandria, Aswan and 

 Meroe all lay on a direct north to south line. These attempts to 

 provide a fixed framework for the world map were criticized 

 by his successors on the ground that the available data were 

 insufficient. Hipparchus, the best of the Greek astronomers, 

 corrected him in detail, and laid the foundation for further 

 progress by compiling a table of latitudes. 



With the progress of more detailed knowledge and the 

 expansion of the known world through the achievements of 

 Alexander the Great and the Romans, a vast mass of detail 

 accumulated for the use of later cartographers, who could 

 thus take up the task outlined by Eratosthenes and Hip- 

 parchus with greater assurance of success. In the second 

 century a.d., two names are outstanding, those of Marinus of 

 Tyre and Claudius Ptolemy of Alexandria. The work of 

 Marinus is known to us almost entirely from Ptolemy's refer- 

 ences to him in his 'Geographical exposition'.^ Marinus 

 developed earlier ideas to construct a network of meridians 

 and parallels, but in his world map he drew them as straight 



^For convenience I refer to this as his 'Geography'. It was essentially 

 a guide to drawing the world map. 



