The reply of the King to this message was made to the Dutch Chambers ten days later. Denouncing the revolt, he declared that he would never yield to "passion and violence." Orders were then issued to Dutch troops under Prince Frederick of Holland to proceed to Brussels and retake the city. The attack was made upon the four gates of the walled city on September 23rd. The Belgians prepared a trap, cunningly allowing the Dutch soldiers to enter two of the gates and retreating towards the Royal Park facing the Palace. Here they rallied and attacked the troops of William from all sides at once. Joined by a strong body of men from Liege they fought for three days with such ferocity that Prince Frederick was beaten back again and again, until he was forced to retreat at midnight of the third day. In the battle six hundred Belgian citizens were slain, and to these men, regarded now as the martyrs of the Revolution, a great monument has been erected in the Place des Martyrs, near the trench in which they were buried. A provisional government was now formed which issued the following notice: "The Belgian provinces, detached by force from Holland, shall form an independent state." Measures were taken to rid the country of the Dutch, who were expelled forcibly across the border. Envoys to Paris and London presented documents to secure sympathy for the new government, while the fight for independence was still going on fiercely. Waelhern and Berchem, besieged by the Belgian volunteers, soon fell, and the city of Antwerp was occupied by them before the end of October. Then the Conference of the Five Powers, sitting in London, interposed to force an armistice in order to determinate some understanding and arrangement between the Dutch and the Belgians, since it had become evident that the Netherlands kingdom of 1815 had practically come to an end. By the treaty of London in 1814, and that of Vienna in 1815, Belgium, after a short interregnum of Austrian rule, was incorporated with Holland into the Kingdom of the Netherlands. In the space of a month then the Belgian patriots had accomplished their task, and on November 18th the National Assembly, convoked, declared as its first act the independence of the Belgians. It was now necessary to find a head upon which to place the crown. The first choice of the provisional government was the Duc de Nemours, the son of Louis Philippe, but objection was made to him on the ground that his selection would add too much, perhaps, to the power of France, so his candidature was withdrawn. Choice was fixed finally upon Prince Leopold of Saxe-Coburg, who had but recently declined the throne of Greece by advice of the European diplomats. A resident of England, this Prince, who had espoused Princess Charlotte, the daughter of George IV, was well known as a most clear headed diplomat, a reputation he enjoyed during his whole career.