A retreat must therefore be made.
The question was, which route should be chosen?
In any case, one of the narrow dikes connecting the island city with the shore must be traversed; and on these causeways the Spaniards would fight under great disadvantage.

Finally, he settled upon that leading to Tlacopan, which was much the shortest, being only two miles in length.
For some days a large party of men had been at work constructing movable towers, similar to those used, centuries before, in sieges.
They moved on rollers, and were to be dragged by the Tlascalan allies.

From their summits the soldiers could shoot down upon the housetops, from which they had been hitherto so annoyed.

The towers were also provided with bridges, which could be let down on to the roofs, and so enable the soldiers to meet their opponents hand to hand.
When the structures were completed, the Spaniards again took the offensive.

The gates were opened, and the three towers, dragged by the Tlascalans, moved out.