But, if such humiliating reflections crowded on his mind, the alternative of remaining, in his present crippled condition, seemed yet more desperate.[137] With his men daily diminishing in strength and numbers, their provisions reduced so low that a small daily ration of bread was all the sustenance afforded to the soldier under his extraordinary fatigues,[138] with the breaches every day widening in his feeble fortifications, with his ammunition, in fine, nearly expended, it would be impossible to maintain the place much longer--and none but men of iron constitutions and tempers, like the Spaniards, could have held it so long--against the enemy. The chief embarrassment was as to the time and manner in which it would be expedient to evacuate the city. The best route seemed to be that of Tlacopan (Tacuba). For the causeway, the most dangerous part of the road, was but two miles long in that direction, and would, therefore, place the fugitives, much sooner than either of the other great avenues, on terra firma. Before his final departure, however, Cortés proposed to make another sally, in order to reconnoitre the ground, and, at the same time, divert the enemy’s attention from his real purpose by a show of active operations. For some days his workmen had been employed in constructing a military machine of his own invention. It was called a _manta_, and was contrived somewhat on the principle of the mantelets used in the wars of the Middle Ages. It was, however, more complicated, consisting of a tower made of light beams and planks, having two chambers, one over the other. These were to be filled with musketeers, and the sides were provided with loop-holes through which a fire could be kept up on the enemy. The great advantage proposed by this contrivance was to afford a defence to the troops against the missiles hurled from the terraces. These machines, three of which were made, rested on rollers, and were provided with strong ropes, by which they were to be dragged along the streets by the Tlascalan auxiliaries.[139]