The launching of the ships was followed by a grand review of the army, never before so strong and well equipped. It mustered now eighty-seven horsemen, eight hundred and eighteen Spanish foot-soldiers, and fifty thousand Tlascalans led by the younger Xicotencatl.

The army was divided into three battalions. The first, under Alvarado, was to take up its quarters at Tacuba, and blockade the western causeway. The second under Olid, was to encamp at Cojohuacan, the city commanding the branch causeway which joined the southern avenue at Xoloc. The third under Sandoval was to march on Iztapalapan, which had been refortified by the Aztecs. Cortés himself intended to take the command of the brigantines.

The Tlascalans who were attached to Alvarado's division were the first to set out. On the road, Xicotencatl, who had from the first nursed in his heart a hatred for the arrogant Spaniards, infuriated by an insult to one of his followers, suddenly abandoned the army and turned back to Tlascala. To the messengers immediately despatched to beg him to return he replied:

"If my father had listened to me he never would have become the dupe of the treacherous strangers."

Continuing on his way the cacique  had almost reached the borders of Tlascala when he heard behind him the ring of iron hoofs. Up dashed the cavaliers, and in a flash Xicotencatl was seized, bound, and carried back to Tezcuco, there to be hanged like a common malefactor. To Tlascala a message was sent informing the elders of the republic that among the Spaniards desertion was always punished with death.

Success seemed ever to wait on the ruthless white men. Alvarado at Tacuba broke down the aqueduct which carried fresh water to Mexico from cypress-crowned Chapoltepec. Sandoval captured Iztapalapan. Cortés with the brigantines waited grimly for the swarm of Aztec canoes which sallied forth from the city on battle intent. Like gnats they gathered round the warships. At this moment a breeze arose, and the Spanish fleet moving forward crashed into the light canoes, breaking and sinking them in every direction, while over the waters far and wide the guns spread havoc and death. The rout was complete. The brigantines, from this time masters of the lake, proved, as Cortés himself said, "the key of the war."

With the aid of the fleet it was easy work to capture the Fort of Xoloc, and at that important point Cortés made his camp. In vain did the Aztecs, fighting day and night, make desperate efforts to retrieve their mistake in leaving such a post so weakly garrisoned. Breaking up a small piece of the causeway, Cortés made a channel for his ships, and the Aztecs, riddled on either side by the terrible guns, were driven back to the city in head-long flight.

The Spaniards held the western causeway of Tacuba, the great southern avenue of Iztapalapan with its branch to Cojohuacan, and now Sandoval was sent with a strong force to blockade the northern dyke. Mexico was thus completely beleaguered, with its causeways in the hands of the strangers and its lake controlled by the all-powerful brigantines.

On the ninth day of the siege was planned a simultaneous assault by Sandoval from the north, Alvarado from the west, and the general himself from the south. Early in the morning Cortés and his infantry marched along the causeway, with the protecting brigantines on either side. The Aztecs strove to make a stout defence at every gap, but were always driven back by the withering fire from the ships on their flanks. The way thus cleared, the Spaniards swam across, while the allies stayed to fill up the breach and make a passage for the artillery and horses.

The causeway was passed and the city entered. Here advance was more difficult, since the brigantines could not sail up the shallow canals. Only before the deadly thunder of the cannon did the Aztecs fall back, and it was hours before the Spaniards fought their way to the great square in the heart of the city. For a moment, as if by one consent, the soldiers halted to gaze at this place of terrible memories. There stood the Old Palace, where rose the great teocalli, the scene of such triumphs and such horrors. But their general was on other thoughts intent: loud and clear rang out his voice, "St. Jago! St. Jago! To the Temple! Forward all!"

Fiercely charged the white men in answer to the battle-cry, carrying all before them. Dashing up the stairways and round the terraces of the teocalli, some of the more daring soldiers gained the summit, tore down the new image of Huitzilopotchli, hurled the frantic priests over the dizzy brink, and descended in triumph only to find their comrades below flying in confusion. The Aztecs had rallied, and the Spaniards were driven headlong across the square, leaving the cannon in the hands of the enemy.

Suddenly above the tumult the Indians heard the tramp of galloping horses coming nearer and nearer down a side street. The cavaliers were upon them! Panic-stricken in their turn, they fled before the charge without noticing in their terror of rider and horse from what a mere handful they were fleeing. As dusk drew on the Spaniards returned in good order along the great street, taking their rescued cannon with them, but pursued by the Aztecs "so rabidly" that the rearguard had hard fighting before the Camp of the Causeway was reached at last in safety.

Well pleased was Cortés with the day's work. He had proved his strength by forcing his way into the very heart of the city, and he had burnt down so many of the fortress-houses that the way would be easier for another assault.

Alvarado and Sandoval had each kept the Aztecs hard at work on the western and northern causeways. They had not, however, been able to enter the city, as they could not, unaided by the guns of the ships, make their way across the breaches. Before the next assault three of the brigantines were sent to each commander.

But three days later Cortés, after hard fighting, once more entered the great square in triumph. With savage joy the Spaniards hurled themselves on the Old Palace and burnt it to the ground! Hard by stood the graceful airy House of Birds, a high building of wood most beautifully carved. During all this strenuous time the Aztecs had tended with utmost care these birds of brilliant colour or exquisite song. Now the Spaniards flung torches at the building, which was in a moment ablaze with flaming banners across the sky. With screams of terror a few of the strong-winged birds of prey burst through the burning lattice-work and, spreading their cramped wings, soared far away from the fated city. Roused to fury, the Mexicans attacked the now retreating destroyers so fiercely that every soldier bore some wound ere he regained the Camp of the Causeway.

In spite of weariness and wounds the Spaniards returned each day to the attack, and always found that the Aztecs, equally untiring, had once more broken down the bridges so laboriously raised, for Cortés could not spare a strong enough guard to protect his work by night.

On the western causeway, which was shorter, Alvarado did station at night-time a strong company to defend the bridge nearest to the city. Their only shelters were flimsy huts which let in the rain and wind, and Bernal Diaz, who was in this division, gives a vivid description of all their hardships. They tried to cure their wounds by burning them with hot oil and binding them with strips of Mexican blanket. But, says the old chronicler, "a soldier named Juan Catalan also healed them by charms and prayers, which, with the mercy of our Lord Jesus, recovered us very fast." Sitting in mud and water they ate their "miserable food of maize and herbs withal! but, as our officers said, such is the fortune of war!"

It was the rainy season, and even the general's own division in the Camp of the Causeway suffered much from the cold and wet. To relieve their misery Cortés set the allies to work on erecting barracks of stone and wood. So wide was the causeway near the Fort of Xoloc that these shelters were constructed to hold two thousand men.

Message after message did Cortés send to Guatemozin offering fair terms of peace, but though food grew scarcer and scarcer in the city the young emperor scorned even to reply to the "perfidious strangers." Too well did the Aztecs remember the treachery of Tonatiuh  to put faith in the promise of a Spaniard!

All that a general could do unaided by warships, cannon, cavalry, and steel weapons, Guatemozin did. Reorganising the old way of Aztec warfare, he made surprise attacks after dark, and kept a strict guard during the night, his warriors relieving each other in Spanish fashion. Simultaneous assaults were made on the three divisions of the besieging army. Open battle with the brigantines had proved useless, so among the tall rushes near the southern shores of the lake an ambush was laid. Stakes were driven into the shallow waters, and then several canoes rowed past the proud warships, tempting pursuit. Two of the smaller brigantines immediately gave chase and were lured into the ambush. Entangled among the stakes they had small chance in the furious fray which followed. Most of the white men were wounded and one of the brigantines was captured.

With such a foe the Spaniards could take no rest. "So ceaseless were our battles," says Bernal Diaz, "by day and by night, during the three months in which we lay before the capital, that to recount them all would but exhaust the reader's patience, and make him to fancy he was perusing the incredible feats of a knight-errant of romance."