Cortés, thus impeded, ordered up a few pieces of heavy ordnance, which soon swept away the barricades and cleared a passage for the army. But it had lost the momentum acquired in its rapid advance. The enemy had time to rally and to meet the Spaniards on more equal terms. They were attacked in flank, too, as they advanced, by fresh battalions, who swarmed in from the adjoining streets and lanes. The canals were alive with boats filled with warriors, who with their formidable darts searched every crevice or weak place in the armor of proof, and made havoc on the unprotected bodies of the Tlascalans. By repeated and vigorous charges, the Spaniards succeeded in driving the Indians before them; though many, with a desperation which showed they loved vengeance better than life, sought to embarrass the movements of their horses by clinging to their legs, or, more successfully, strove to pull the riders from their saddles. And woe to the unfortunate cavalier who was thus dismounted,--to be despatched by the brutal _maquahuitl_, or to be dragged on board a canoe to the bloody altar of sacrifice! But the greatest annoyance which the Spaniards endured was from the missiles from the _azoteas_, consisting often of large stones, hurled with a force that would tumble the stoutest rider from his saddle. Galled in the extreme by these discharges, against which even their shields afforded no adequate protection, Cortés ordered fire to be set to the buildings. This was no very difficult matter, since, although chiefly of stone, they were filled with mats, cane-work, and other combustible materials, which were soon in a blaze. But the buildings stood separated from one another by canals and draw-bridges, so that the flames did not easily communicate to the neighboring edifices. Hence the labor of the Spaniards was incalculably increased, and their progress in the work of destruction--fortunately for the city--was comparatively slow.[116] They did not relax their efforts, however, till several hundred houses had been consumed, and the miseries of a conflagration, in which the wretched inmates perished equally with the defenders, were added to the other horrors of the scene.