Astorga was located on the flank of the French invasion of Spain and Portugal, and was meant to be used as a headquarters during the campaign.

[4] Junot arrived at Astorga on March 21 with Napoleon's 8th corps, consisting of 12,000 men, including 1,200 cavalry forces.

[3] Junot placed Bertrand Clausel's division in the position Loison had held,[7] with Solignac in support, and St. Croix to watch the rear.

[4] General Loison attempted to take the city in February 1810, as it was meant to be his headquarters during the invasion of Portugal; but was unprepared to attack the defenses he found there, and was forced to retreat.

[8] During these weeks, Santocildes emptied the town of 3,000 of its residents and stocked up on supplies for the siege,[4] which began on March 21 of 1810.

[11] Until the siege guns arrived, there was no action except nuisance fire from what little artillery Junot had,[7] and skirmish parties sent out from Astorga.