On May 12 Lord Roberts entered Kroonstad. In his advance, averaging thirteen miles per day, he had outstripped the reconstruction of the railway, of which almost every bridge and culvert had been blown up by the retreating Boers, and many miles of the permanent way had been destroyed. A halt was therefore necessary until the railhead could be brought nearer, and to give the Army an opportunity of pulling itself together, which was especially required by the cavalry. Little more than one-half of the 6,000 horses with which French marched out of Bloemfontein on May 6 were fit for service at Kroonstad seven days later. Ian Hamilton was sent out in chase of the flitting Free State Government. He found it not at Lindley, nor at Heilbron, for it had trekked away to Frankfort. Between Lindley and Heilbron he was attacked in rear by a body of Boers, who emerged from the presumed vacuum behind him, but they were beaten off. The bulk of the enemy's force which had evacuated Kroonstad, was now in the triangle formed by the railway, the Vaal and the Rhenoster. On its left flank was Ian Hamilton; and French was ordered out to hook the right flank, a repetition of the movement which had failed at Zand River. On May 22 Lord Roberts left Kroonstad. The enemy, however, again evaded the net. Reconnaissances by French on May 23 showed that Botha had been frightened by the appearance of Ian Hamilton at Heilbron, and had crossed into the Transvaal. The discovery necessitated the recasting of Lord Roberts' plan, and brought about an interesting and entirely successful strategic movement. It was evident from Botha's dispositions that he expected Ian Hamilton to march straight to his front and endeavour to cross the Vaal above the railway bridge at Vereeniging. The difficult drifts and country below it were considered to be a sufficient protection, and were not strongly held by Botha, who on this occasion was completely out-generalled by his opponent. Lord Roberts ordered Ian Hamilton to march from the right flank to the left, across the front of the main Army, and then in conjunction with French to wheel round to Meyerton on the line between Johannesburg and Vereeniging. On the evening of May 26 he entered the Transvaal at Wonderwater Drift. But Ian Hamilton's column had not the honour of being the first troops of the main body to enter the Transvaal, for he found the cavalry in front of him. French,[43] who had been sent out from Kroonstad on May 20, reached the Vaal at Paris on the 24th, and at once threw part of his force into the Transvaal, the rest crossing higher up at Old Viljoen's Drift. He thus fittingly celebrated the last birthday festival of Queen Victoria, which was also appropriately honoured by a proclamation issued on the same day by Lord Roberts, by which the Orange Free State was annexed to the dominions of Her Majesty under the designation of the Orange River Colony--a suitable birthday offering from a distinguished soldier to his Sovereign.