Such then may be accepted as a picture of one of the numerous pilgrimages made during the Dark Ages and which helped to spread infectious diseases broadcast throughout the land, polluting water supplies to such an extent that in many localities filth diseases became epidemic. It was not until about the end of the sixteenth century that general improvement began to be made in sanitary matters, although some notable exceptions may be mentioned in the construction of a few important works in Spain by the Moors, such for instance as those at Cordova in the ninth century and the repair of the Roman aqueduct at Sevilla in 1172. Until as late a date as 1183 Paris depended entirely on the River Seine for its water supply. During that year an aqueduct was constructed to conduct water to Paris from a distant source, but as late as the year 1550 the supply of water to Paris amounted to only one quart per capita per day. [Illustration: Zempoala Aqueduct. From an old print in the _Engineering News_] London, England, was more backward than Paris in supplying the inhabitants with water, and it was not until the year 1235 that small quantities of spring water were brought to the city through lead pipes and masonry conduits. Little is known about the strange race of people that inhabited the North American continent prior to the Indians, and it is only by the ruins of works which they constructed in the shape of mounds that their existence is known of. Nevertheless, had historians of that time written of the engineering projects successfully carried out by the engineers of the mound builders no doubt some surprising facts would be revealed to contemporary man; for wherever men have existed, whether in China, Japan, Egypt, Europe, England or, as we are informed by astronomers, on Mars, gigantic works of irrigation have been successfully undertaken, and in most of the places mentioned conduits or aqueducts to supply water to inhabitants of communities were constructed. Reasoning then by analogy it would be safe to infer that before the race of mound builders became extinct they built works of equal importance if not of equal endurance. This belief is borne out by the fact that long before Columbus discovered America, the Aztecs of Mexico built an aqueduct to supply the ancient city, built on the site of the present City of Mexico. How long the aqueduct supplied the city before Cortez, in his expedition to conquer Mexico, destroyed the works, in 1521, nobody knows and the truth will probably never be told. The fact of the existence of such a structure is interesting chiefly as showing that in the matter of supplying communities with water the ancient tribes of Mexico and America had made considerable progress long before Europeans set foot on shore. It was in Mexico, too, that the next aqueduct in point of time was constructed. This work was built during the period between the years 1553 and 1570, under the