Adam Clarke on Joshua 6:1

Now Jericho was straitly shut up - The king of Jericho, finding that the spies had escaped, though the city was always kept shut by night, took the most proper precaution to prevent every thing of the kind in future, by keeping the city shut both day and night, having, no doubt, laid in a sufficiency of provisions to stand a siege, being determined to defend himself to the uttermost.