Cortés next arranged the order of march. The van, composed of two hundred Spanish foot, he placed under the command of the valiant Gonzalo de Sandoval, supported by Diego de Ordaz, Francisco de Lujo, and about twenty other cavaliers. The rear-guard, constituting the strength of the infantry, was intrusted to Pedro de Alvarado and Velasquez de Leon. The general himself took charge of the “battle,” or centre, in which went the baggage, some of the heavy guns, most of which, however, remained in the rear, the treasure, and the prisoners. These consisted of a son and two daughters of Montezuma, Cacama, the deposed lord of Tezcuco, and several other nobles, whom Cortés retained as important pledges in his future negotiations with the enemy. The Tlascalans were distributed pretty equally among the three divisions; and Cortés had under his immediate command a hundred picked soldiers, his own veterans most attached to his service, who, with Cristóval de Olid, Francisco de Morla, Alonso de Avila, and two or three other cavaliers, formed a select corps, to act wherever occasion might require. The general had already superintended the construction of a portable bridge to be laid over the open canals in the causeway. This was given in charge to an officer named Magarino, with forty soldiers under his orders, all pledged to defend the passage to the last extremity. The bridge was to be taken up when the entire army had crossed one of the breaches, and transported to the next. There were three of these openings in the causeway, and most fortunate would it have been for the expedition if the foresight of the commander had provided the same number of bridges. But the labor would have been great, and time was short.[170] At midnight the troops were under arms, in readiness for the march. Mass was performed by Father Olmedo, who invoked the protection of the Almighty through the awful perils of the night. The gates were thrown open, and on the first of July, 1520, the Spaniards for the last time sallied forth from the walls of the ancient fortress, the scene of so much suffering and such indomitable courage.[171]