The fiercest fight during the siege was on June 4. The garrison had dug a ditch, and thrown up a bank across the Windmill Hill, which protected St. Columb's Wells. These were very important, for the wells inside the walls were made turbid by the constant firing. The windmill itself, which still stands, had been strengthened by earthworks, and two or three small guns were mounted on it. Hamilton ordered nearly all his available infantry and some cavalry to advance against the bank, which for the most part was about twelve feet high. No attempt was made to loosen the newly made work, there were no ladders, and the foot-soldiers were quite unable to surmount the obstacle. They fell fast under the fire of the besieged, whose fowling pieces carried farther than their muskets. Only one-third of the defenders fired at a time, and thus a continuous hail of bullets was kept up. The assailants' right wing of cavalry was commanded by Colonel Edmund Butler, Lord Mountgarret's eldest son. He was exceptionally well mounted, and galloped to the top of the bank, which at the waterside did not exceed seven feet. On descending within the enclosure he was at once made prisoner. About thirty men tried to follow, but only two officers jumped successfully, one of whom was killed, the other escaping after his horse had been shot under him. Of the Irish, at least 200 were killed, besides many officers, the besieged only losing one officer and six men.[224] [Sidenote: An English squadron appears,] [Sidenote: but is forced to retire.] [Sidenote: Schomberg interferes.] [Sidenote: Debate in the English Parliament.]