The first alternative was to march southeast to the River Kennet and cross it, going through Newbury and returning to Reading's fortifications, thus evading the Royalists and allowing for a safe retreat to London. The disadvantage to this was the time it would take to cross the relatively open land between Essex's position and the Kennet. The second, and the option Essex initially took, was to go north, either to make battle in more advantageous circumstances or to evade the Royalists. If Essex was able to cross to the west bank of the River Avon, he could secure the bridges across it and prevent the Royalists from crossing it and confronting his army. His cavalry advanced to Upton to screen the main force from Royalist interference on 11 September, with the rest of the soldiers quickly following. The Royalists were left wrong-footed; Charles did not discover Essex's retreat for another 24 hours, during which the gap between the armies widened. The Royalists finally began to march on 16 September, with Rupert's cavalry streaming ahead to try to disrupt the Parliamentarian retreat.