266 GEOGRAPHICAL SCIENCE. 



Livy and Julius Csesar, were also geographers ; and Pliny the Elder summed 

 up, in his four books of "Natural History," all the results obtained by 

 geographical research, and set forth in a number of works no longer extant. 



Pliny often mentioned in his " Natural History " the geodesical operation 

 attributed to Marcus Vipsanius Agrippa, prime minister and son-in-law of 

 Augustus. It was Julius Caosar who, during his consulship (according to 

 the positive assertion of Ethicus, a geographer of the fourth century), 

 "ordered by a senatiis-comultum that the whole Roman world should be 

 measured by men of the greatest ability and endowed with all sorts of 

 knowledge." This vast enterprise, intrusted to four Greek mathematicians 

 and geographers, Zenodoxus, Theodotus, Polyclitus, and Didymus, who had 

 under their orders a staff of geodesical measurers and land surveyors, was 

 completed in twenty-five years. It would appear that Agrippa took the 

 matter in hand, and when it was completed he proposed to construct at 

 Rome a gigantic portico, beneath which he intended to " unfold the map 

 of the world before the eyes of the universe," as Pliny expressed it. The 

 premature death of this illustrious general prevented the execution of this 

 grand project, but the map of the Roman world, with the roads and distances 

 indicated, was deposited in the archives of the Senate (Fig. 192). 



Nor was the progress of geography assisted by the victorious armies 

 alone, for the travellers, and still more the merchants, whose vessels, even at 

 that period, conveyed them to the most distant parts and brought back cargoes 

 from the ports of India, did much towards the same end. Under the reign of 

 Nero, two centurions were sent by the Emperor to Ethiopia in search of the 

 sources of the Nile, and this expedition is alluded to by Seneca and Pliny. 

 Previously to this, during the reign of Claudius, a Greek philosopher of Egypt, 

 one Hippalus, had struck out with his vessel from the coast, and ventured 

 across the high seas, starting from the Gulf of Adulis (Aden), and arriving 

 upon the coast of India. Another traveller, named Diogenes, was driven by 

 north winds as far as a large island called Menuthias, otherwise Zanzibar. 

 From this time forward all the coast-line was marked upon the marine maps, 

 but the Erythrean Sea (as the Indian Ocean was then called) was believed to 

 be impassable and full of terrible dangers, though more than one Egyptian 

 or Phoenician sailor had endeavoured to sail across it. 



One of these experienced pilots, Marinus of Tyre, carefully collected all 

 the geographical information which he could gather from the maritime com- 



