It must not be supposed, that, having reached the island, the Spaniards could exchange the narrow and ditched causeways for firm and spacious streets. On the contrary, the causeways, so to speak, were continued up to within half a mile of the principal square which was in the very centre of the city, and contained the great pyramid, as well as the chief temples of Mexico. On either side was a canal both broad and deep, dividing the road from the houses; and others, running from intersecting streets, perforated the causeways with chasms, the number of which the Mexicans had long since greatly increased. The island, which was circular, did not exceed three miles in diameter, of which the central third only was dry and solid. Hence the advanced posts of the three divisions were at no considerable distance from each other; and if the call of Cortes in the morning was not absolutely heard and answered by his two lieutenants, the bugles of each could be easily distinguished, cheering one another as they advanced to the daily assault. The labour of Cortes in destroying the suburb in his quarter, was less than that of the others; for here, the lake being deeper, the houses extended but a short distance from the island. His advanced post was almost within the limits of the suburb, and separated from the island by only one ditch, which he had twice or thrice taken and filled up, but was as often obliged to yield again to the foe, subduing his impatience, until his lieutenants had advanced equally far in their quarters. The outposts were always guarded with the most jealous vigilance, particularly in the later hours of the night, after the rains, which, in this climate, commonly prevail with the greatest violence between the hours of noon and midnight. A guard of forty men, with two pieces of artillery, kept watch until midnight; when, yielding their places to forty more, but not retiring, they threw themselves to sleep upon the damp stones and clay. Two hours before dawn, the post was strengthened by another company of forty, who watched until morning, the others flinging themselves in their cloaks among the first watchmen. Thus, there were ready, before day, one hundred and twenty men, the strongest and boldest of their divisions, who, in case of sudden attack, could preserve the station, until reinforced by the whole strength of the division, from the towers of the gates, which were still the head-quarters of the several divisions. The causeway between the gates and the pickets, was occupied by patrols of horsemen, who watched lest the enemy, coming in canoes, should make a descent behind the advanced post, and thus cut it off.