As to the points from which his attacks were to be launched, they were undoubtedly the best under the circumstances, though, had he wished, he could have selected a fourth, thereby launching his men along each end of the main causeway, and by each one of the branches which led into it. But he was too astute to block up the path of retreat. He recognised that even with all his allies he had an enormous host to contend with, and that all were filled with desperation and determination. His spies had told him that, and also that amongst the allies who had come into the city there were some who, like those outside, might in time waver. It would be wise policy to give them a free outlet to escape, and thereby reduce the numbers of the defenders. And to further this solution he took care to send messages to these friends of the Mexicans, offering every inducement to cause them to waver in their allegiance. His arrangements made, as Teotlili had correctly reported, Cortes no sooner saw the aqueduct destroyed, than he sent his divisions to their posts, and caused the brigantines to be floated. A glance at the plan of Mexico will show the camps of the Spaniards, and the reader will be able to see the construction of the causeways. One running directly from shore to shore, through the heart of the city, while a second--that by which Pedro de Alvarado was to force an entrance--cut out from the shore to what might be described as the back of Mexico. For this fine city was situated at one end of the lake, within easy distance of the shore to which the causeways connected it, while its face might be said to look out to the vast expanse of salt lake on which the brigantines had just been floated. And these latter could attack this side alone and the long causeway running through the heart of the city, for the latter presented a barrier through which only canoes could pass. There were three other causeways or viaducts, one of which De Olid was to march by, while the other two were small and insignificant, and ran from the north-western shore. A few words will describe the preparations of the defenders, many carried out at the suggestion of Roger. Numerous breaches had been constructed along the causeways, planks being left for the use of the Mexicans. Then barricades had been built of sun-dried bricks at the back of these breaches, and crossbow shafts piled there, with an ample supply of lances and other weapons. Canoes lay on either side, ready to hamper the attackers in every possible manner, while all carried long poles with hooks at the end.