By 24 August, the Royalists, suffering from shortfalls in their stocks of gunpowder and cannonballs, remained unable to breach the walls. Essex, in the meantime, had been urgently preparing his army, which thanks to disease, indiscipline and desertion numbered less than 6,000 infantry and 3,500 cavalry. This was not a force strong enough to defeat the Royalists, and so he demanded an extra 5,000 soldiers; Parliamentarians in London responded by enlisting the London Trained Bands, which provided an additional 6,000 men. Taking into account additional problems and desertions, the eventual force was 9,000-foot soldiers and 5,000 cavalry. After being mustered on Hounslow Heath, the army began marching towards Aylesbury, arriving on 28 August. This force was formally mustered on 30 August, and after being reinforced by Lord Grey on 1 September at Brackley, marched to Gloucester. On 5 September, with heavy rain falling, the Parliamentarian army reached the town and camped on Prestbury Hill, immediately outside it; their presence forced the Royalists to abandon the siege given that neither army, wet and exhausted, was in a state to seek battle.