After the Battle of Lostwithiel in August 1644 at which the Royalists forced the Parliamentary forces led by the Earl of Essex to retreat to Plymouth, King Charles left Cornwall taking the majority of his army with him including the Cornish regiments that had been raised in 1642. Concerned that Essex's garrison at Plymouth was a continued threat to the south west, it was decided that the town should be blockaded and Richard Grenville (1600–1658) was selected for this task.