VIII 



ARTIFICIAL STONE, OR CONCRETE 



1 



*MIE Greeks and Romans were not the only 

 ancient people who had learned to use some 

 kind of cement as a substitute for rock in 

 building. The Mexicans in the Western hemisphere 

 are known to have used it extensively in some of their 

 constructions. But none of these cements had exactly 

 the composition of the modern Portland cements, whose 

 superiority makes possible the wonderful present-day 

 building operations. The endurance of the dome of 

 the Pantheon through two thousand years would seem 

 to disprove any contention that Roman concrete needed 

 anything in the way of improvement. Yet it is un- 

 doubtedly true that Portland cement is far superior to 

 the Roman "puzzolana," as it is called, for most 

 purposes. It has greater resistance to crushing, and 

 is not affected to so great an extent by oxidation in a 

 dry atmosphere. 



Through the action of volcanoes, Nature placed 

 material for cement in the very dooryard of the Ro- 

 mans. The volcanic dust found near the village of 

 Pozzuoli, when added to lime could be transformed 

 into a cement which would set under water, and be as 

 enduring as rock itself. The Romans called this 



