The three columns advanced simultaneously. The Spanish pressed the Aztecs back before them. Their allies filled up the canals as they took them, one by one. The Tlascalans stormed the houses, and attacked the enemy on their roofs; while the canoes engaged those of the Aztecs, and so prevented them from interfering with the men occupied in filling up the breaches. The parallel streets were near enough to each other for the Spaniards to hear the shouts of their companions in the other columns, and to know that all were gaining ground steadily. The enemy in the streets fought with less obstinacy than usual; and Cortez, with his usual keen-sightedness, at once apprehended that the feebleness of the resistance indicated some device, and that the Aztecs were allowing them to advance, only to lead them into a trap. He had received a message from Alderete saying that he was getting on fast, and that he was but a short distance from the great square. Fearing that this officer, eager to be the first to gain the marketplace, was not taking proper precautions to secure his retreat; Cortez, with a small body of troops, retraced his steps, and turned up the street by which Alderete's column had advanced. He had gone but a short distance, when he saw that his stringent orders had been neglected; for he came upon an opening some thirty feet wide, full of water at least twelve feet deep. A slight attempt, only, had been made to stop the gap; and stones and timber, lying by the side, showed that it had been abandoned as soon as commenced. The general saw, too, that the road had been narrowed as it approached this point, and that the work had evidently been recently done. Much alarmed at the consequence of this neglect, he at once set his men to fill up the breach; but they had scarcely begun the operation when a terrific yell arose, drowning the mingled clamor of the distant conflict. Alderete had, as Cortez supposed, pressed on the retreating Aztecs with too great eagerness. He had carried the barricades which defended the breach, and had given orders that the chasm should be filled up. But in their eagerness to be first in the square, the Spaniards had pressed on, none caring to stop to see that the allies carried out the order. So, taking position after position, they pressed on until they were close to the square. Suddenly the horn of Guatimozin, the emperor, sent forth a piercing note from the summit of a temple. As if by magic, the retreating Aztecs turned and fell on their pursuers; while swarms of warriors from the adjoining streets, lanes, and corners attacked the advancing column.