The Prince of Orange, meanwhile, encouraged the citizens to persevere, by frequent promises of assistance.  His letters, written on extremely small bits of paper; were sent into the town by carrier pigeons.  On the 28th of January he despatched a considerable supply of the two necessaries, powder and bread, on one hundred and seventy sledges across the Harlem Lake, together with four hundred veteran soldiers.  The citizens continued to contest the approaches to the ravelin before the Cross-gate, but it had become obvious that they could not hold it long.  Secretly, steadfastly, and swiftly they had, therefore, during the long wintry nights, been constructing a half moon of solid masonry on the inside of the same portal.  Old men, feeble women, tender children, united with the able-bodied to accomplish this work, by which they hoped still to maintain themselves after the ravelin had fallen: 

On the 31st of January, after two or three days’ cannonade against the gates of the Cross and of Saint John, and the intervening curtains, Don Frederic ordered a midnight assault.  The walls had been much shattered, part of the John’s-gate was in ruins; the Spaniards mounted the breach in great numbers; the city was almost taken by surprise; while the Commander-in-chief, sure of victory, ordered the whole of his forces under arms to cut off the population who were to stream panic-struck from every issue.  The attack was unexpected, but the forty or fifty sentinels defended the walls while they sounded the alarm.  The tocsin bells tolled, and the citizens, whose sleep was not-apt to be heavy during that perilous winter, soon manned the ramparts again.  The daylight came upon them while the fierce struggle was still at its height.  The besieged, as before, defended themselves with musket and rapier, with melted pitch, with firebrands, with clubs and stones.  Meantime, after morning prayers in the Spanish camp, the trumpet for a general assault was sounded.  A tremendous onset was made upon the gate of the Cross, and the ravelin was carried at last.  The Spaniards poured into this fort, so long the object of their attack, expecting instantly to sweep into the city with sword and fire.  As they mounted its wall they became for the first time aware of the new and stronger fortification which had been secretly constructed on the inner side.  The reason why the ravelin had been at last conceded was revealed.  The half moon, whose existence they had not suspected, rose before them bristling with cannon.  A sharp fire was instantly opened upon the besiegers, while at the same instant the ravelin, which the citizens had undermined, blew up with a severe explosion, carrying into the air all the soldiers who had just entered it so triumphantly.  This was the turning point.  The retreat was sounded, and the Spaniards fled to their camp, leaving at least three hundred dead beneath the walls.  Thus was a second assault, made by an overwhelming force and led by the most accomplished generals of Spain, signally and gloriously repelled by the plain burghers of Harlem.