In the months of May and June, 1644, Lancashire for the first time became involved in the general course of the war, and for some weeks it was the centre of most important events. So much of other than merely local interest had the first siege of Lathom House, that it influenced the course of Rupert's march north, which was made in order to effect a junction with the Earl of Newcastle to check the Scotch army which was now on its way to the assistance of the Parliament. The Scots, 21,000 strong, under Alexander Leslie, Earl of Leven, had crossed the Tweed on January 19, 1643-4. Newcastle at once summoned Rupert to come to his aid, and marching northwards occupied the town of Newcastle; but he was soon obliged to fall back on Durham. Meanwhile Sir Thomas Fairfax, after the battle of Nantwich on January 25th, had rejoined his father in Yorkshire, and the two soon began to recover the county for the Parliament. On April 11th they stormed Selby, taking among other prisoners Lord Bellasis, whom Newcastle had left in command during his absence. This defeat obliged Newcastle to retreat still further southwards, and he shut himself up in York which was blockaded by Fairfax and the Scots on April 22nd.[137] In January of this year Rupert had captured Aylesbury, and early in March he set out to relieve Newark which had been invested by the Parliament. The siege was raised, and the besiegers, who were commanded by Sir John Meldrum, were forced to capitulate; but Rupert had to return his troops to the garrisons from which he had borrowed them, and almost without an army he marched back to the Welsh border, where he occupied himself with raising fresh troops to go to the assistance of the Earl of Newcastle. As soon as his intentions for the north were known, the Earl of Derby endeavoured to persuade him to march by way of Lancashire in order to relieve Lathom House. The besieged Countess must have written to her husband in a very different tone from that of her defiant answers to Rigby; indeed if the Earl of Derby did not unduly exaggerate the position of the garrison, they must have been in imminent fear of being compelled to surrender. The petition was, however, seconded by the Lancashire royalists, and the Earl of Derby promised that if Lathom were relieved he would aid Rupert's further march with 2,000 men and a considerable sum of money. It was pointed out that the towns of Liverpool and Warrington were but weakly garrisoned, and that the reconquest of Lancashire would be a great gain for the King's cause in the north of England, "the rebellion in those parts being wholly supported from there." Liverpool would be of immense use as the port towards Ireland, and Derby and Prince Rupert had already discussed over the map the possibility of reducing it.[138]