St. Ruth, believing that the tower could not long withstand the terrible fire brought to bear on it, set to work in the erection of earth-works to answer the same end, and for this purpose he conveyed some guns outside the town, and erected two batteries--one to the north and the other to the south--both bearing across the eastern angles of the bridge. Their fire soon drove the English gunners from their batteries, and during the cessation of their fire two intrenchments were thrown up on a high ground to the right and left of the castle. The fire from these dislodged the English musketeers from the walls near the river, and from this forward the contest became a duel of artillery. Ginckle's heavy missiles still bore down all obstructions; the ingenious traverse and change of position were unavailing; nothing could withstand the heavy guns of the besiegers but the Connaught Tower, and that, though crumbling bit by bit, still sent its shot with the same precision as before. In this manner the conflict raged during the whole of the 27th. The bombs of the enemy became exhausted, but this brought no respite to the besieged. Immense blocks of stone, even more destructive than shell, were hurled into the Irish intrenchments, crushing their fascines to atoms, and breaking down all barriers. Towards evening a body of the besiegers, moving behind an improvised breastwork, stormed the bridge, gained possession of the broken arch, and secured themselves behind a strong breastwork. The defence was stubborn, and cost both sides dearly; "for," says the English annalist, "what we gained here was inch by inch, as it were, the enemy sticking very close to it, though great numbers of them were slain by our guns, and the service cost us a great store of ammunition." But ammunition was of small account with Ginckle. One hundred wagon-loads of shot and shell reached the camp that evening; thirteen squadron of wagon-horses were sent to Dublin for more, and two batteries were added to the seven that had been at work since the morning of the 25th. One of these was on a hill outside the wall, which commanded the western end of the bridge, and the other in a meadow to the south of it, which raked the passage leading from the Irish town to the castle. Under cover of these nine batteries the English reached the last broken arch, and secured themselves by a breastwork overlooking that of the Irish on the other side. Here the grenadiers of both armies now stood firing their muskets and hurling their grenades across the narrow space that separated them. At length the fascines of the Irish breastwork took fire, the whole was soon a sheet of flame, its defenders were forced to retire, and on the night of the 27th the English remained masters of the last broken arch of the bridge.