Here William remained a week to improve the defences of the castle, during
which time an epidemic suddenly struck the army and caused some deaths. Usually
ascribed to dysentery, it may from the evidence, according to a recent medical
opinion, have been gastro-enteritis due to contaminated food or water, or both.
About one-third of the army, some 1,700 men, did not take part in the next marches.
On 31 October, leaving a garrison of one company of infantry and all the sick
at Dover, the army moved to both sides of Canterbury.--Whitelock