The junction of the four thousand Castilians, of whose approach he had heard, with Las Torres would raise the force under that general to a point which would enable him to blockade the town pending the arrival of artillery for siege works; and no sooner had the earl returned to his quarters, after seeing the cannon placed upon the walls, than he began his preparations for another expedition.

He ordered Colonel Zinzendorf to march quietly out of the city at eight o'clock with four hundred of his dragoons, and four hundred British and as many Spanish infantry were to join him outside the walls.

The colonels of these three bodies were ordered to say nothing of their intended movement, and to issue no orders until within half an hour of the time named.

At the same hour the rest of the troops were to march to the walls and form a close cordon round them, so as to prevent any one from letting himself down by a rope and taking the news that an expedition was afoot to Las Torres.
At a few minutes past eight, eight hundred foot and four hundred horse assembled outside the gates, and Peterborough took the command.

His object was to crush the Castilians before they could effect a junction with Las Torres.