One of the chief features of Mexico city was the series of causeways which connected the island with the mainland. The position of these, according to the most recent ideas, can be seen in Fig. 1, p. 13. In building them a double palisade was first constructed, and the space between filled with stones and earth faced with rubble. The great dyke which ran from Iztapalapa to Atzacualco, built by the first Montecuzoma on the advice of Nezahualcoyotl, was no less than ten miles long, and was perforated by sluices, by means of which an attempt was made to control the inundations to which Mexico was subject. The effect of this feat of engineering was to cause the portion of lake to the west, called the Lake of Mexico, to become fresh, and to be filled with wild-fowl and fish, for the springs which fed it contained no salt, whereas the streams running into the eastern portion still continued to carry into it the salt which they absorbed on their journey. Another work of economical importance was the double stone aqueduct which brought water to the city from Chapultepec. The Mexicans also constructed roads in various directions throughout the country, for the use of merchants, couriers, and others who travelled on state business. Such roads were narrow, of well-beaten earth, and often had a watercourse running along the side. Like the Peruvian rulers, the Mexican kings maintained a system of trained runners established at definite posts along certain roads. Messages and light burdens could be transferred long distances in a short time by this method, and we hear of three hundred miles being covered in a day. [Illustration: FIG. 29.--The education of children. _Left._ Girl learning to spin, and boy being shown the use of fishing-implements; age 7 years; daily ration a loaf and a half. _Right._ Girl being punished with aloe-spines (age 9 years, omitted); boy being held over a fire of pepper (age 11 years, omitted). Same daily ration. (_Mendoza MS., Oxford_)]