The rude founders of Tenochtitlan built their frail tenements of reeds and rushes on the group of small islands in the western part of the lake. In process of time, these were supplanted by more substantial buildings. A quarry in the neighborhood, of a red porous amygdaloid, _tetzontli_, was opened, and a light, brittle stone drawn from it and wrought with little difficulty. Of this their edifices were constructed, with some reference to architectural solidity, if not elegance. Mexico, as already noticed, was the residence of the great chiefs, whom the sovereign encouraged, or rather compelled, from obvious motives of policy, to spend part of the year in the capital. It was also the temporary abode of the great lords of Tezcuco and Tlacopan, who shared, nominally at least, the sovereignty of the empire.[311] The mansions of these dignitaries, and of the principal nobles, were on a scale of rude magnificence corresponding with their state. They were low, indeed,--seldom of more than one floor, never exceeding two. But they spread over a wide extent of ground, were arranged in a quadrangular form, with a court in the centre, and were surrounded by porticoes embellished with porphyry and jasper, easily found in the neighborhood, while not unfrequently a fountain of crystal water in the centre shed a grateful coolness through the air. The dwellings of the common people were also placed on foundations of stone, which rose to the height of a few feet and were then succeeded by courses of unbaked bricks, crossed occasionally by wooden rafters.[312] Most of the streets were mean and narrow. Some few, however, were wide and of great length. The principal street, conducting from the great southern causeway, penetrated in a straight line the whole length of the city, and afforded a noble vista, in which the long lines of low stone edifices were broken occasionally by intervening gardens, rising on terraces and displaying all the pomp of Aztec horticulture. The great streets, which were coated with a hard cement, were intersected by numerous canals. Some of these were flanked by a solid way, which served as a foot-walk for passengers, and as a landing-place where boats might discharge their cargoes. Small buildings were erected at intervals, as stations for the revenue officers who collected the duties on different articles of merchandise. The canals were traversed by numerous bridges, many of which could be raised, affording the means of cutting off communication between different parts of the city.[313]