But while the arts of civilisation were being fostered on those southern plateaux of the Andes, another seat of native American civilisation had been founded on the corresponding plateaux of the northern continent, and the Aztecs were building up an empire even more marvellous than that of the Incas. The site of the latter is among the most remarkable of all the scenes consecrated to such memories. On the lofty table-land which lies between the Gulf of Mexico and the Pacific Ocean, at an elevation of nearly seven thousand five hundred feet, the valley of Mexico lies engirdled by its ramparts of porphyritic rock, like a vast fortress provided by nature for guarding the infancy of American civilisation. Here was the scene of the heroic age of Toltec Art, where the foundations of all later progress were laid, and architecture achieved its earliest triumphs in the New World on the temples and towers of Tula, the ruined remains of which attracted the attention of the Spaniards at the time of the Conquest. But the history of the Toltecs and their ruined edifices stands on the border lines of romance and fable, like that of the Druid builders of Carnac and Avebury. To them, according to tradition and such historical evidence as is accessible, succeeded their Aztec or Mexican supplanters, along with the Acolhuans, or Tezcucans, as they were latterly called from their capital Tezcuco. Mr. Edward B. Tylor describes an ancient arch which still stands there. It is a skew-bridge of twenty feet span, built with slabs of stone set on edge in the form of a roof resting on two buttresses; and is an ingenious approximation to the true arch.[82] On the opposite shores of the same Mexican lake, the largest of five inland waters that diversified the surface of that great table-land valley, stood Tezcuco and Mexico, the capitals of the two most important states within which the native civilisation of the North American continent developed itself. From the older Toltecans, the encroaching Tezcucans are believed to have derived the germs of that progress, which is best known to us in connection with the true Aztec or Mexican state. Legends of the golden age and heroic races of Anahuac abound, and have been rendered into their least extravagant forms by the patriotic zeal of Ixtlilxochitl, a lineal descendant of the royal line of Tezcuco. But the true Mexicans are acknowledged to be of recent origin, and the founding of Mexico is assigned to A.D. 1326. Among the special evidences of their civilisation is their calendar. By the unaided results of native science the dwellers on the Mexican plateau had effected an adjustment of civil to solar time, so nearly correct that when the Spaniards landed on their coast, their own reckoning, according to the unreformed Julian calendar, was nearly eleven days in error, compared with that of the barbarian nation whose civilisation they so speedily effaced. But the difference thus