Surprise and treachery
Despite formalities in siege warfare, some less then straightforward methods were employed to achieve success, such as the use of spies.
Beggars in the siege lines around Ballon informed the garrison that Fulk of Anjou's men were at dinner, enabling the defenders to launch a highly successful sortie.
In 1364 a monk who carried protection money to La Charit'e-sur-Loire heard the plan to attack Sancerre, the names of captains and strongholds round La Charite, strengths of contingents and the time they would cross the river. He turned out to be the brother of Guichard Aubergeon, the captain of the garrison of Sancerre, and specially chosen. The attackers were subsequently ambushed and cut to pieces.
Despite the presence of sentries in castle towers there are a number of instances of castles being taken by surprise.
There might be a logical explanation; William II seized Mantes in 1097 because the garrison had gone to asses the damage done to the corn and vines the previous day, and were caught as they re-entered. Occasionally a straightforward trick was employed. In 1271 Sultan Baibars forged a letter which ordered the Hospitallers to hand over Krac des Chevaliers.
Others were more daring; in 1364 Bascot de Maul'eon hid with six others in a haystack near Thurie and next morning, dressed as women, they mingled with those filling pitchers at the spring before walking in with kerchiefs over their faces and blowing a horn for their hidden comrades. Similarly in 1401 the Tudor brothers sent a carpenter into Conway who, appearing to arrive for work, slew the two watchmen and seized the castle with 40 others.
However surprise was often the result of treachery. Sometimes this took the form of a simple refusal to respect the code of chivalry, as when the Anjevin count, Geoffrey Martel, was shot in the arm by a crossbowman on the wall as he discussed peace terms during a parley before Cand'e in 1106, a wound from which he subsequently died.
Often though it was the result of a betrayal of one's lord, which to a knight of honour was a particularly base action. The totally ruthless Robert of Belleme used the general confusion following the death of William I to change sides and so capture several castles whose garrisons thought him to be a supporter of the king.
Henry I apparently could not support a long siege for fear of treachery, which always dogged conflicts between kinsmen. At Bures he placed Breton and English mercenaries in the castle since he mistrusted many Normans.
The royal garrison at the fortified manor of the Archbishops palace at Andely were caught of guard when it was betrayed to the French in 1119; soldiers hiding in the straw in a corn storehouse rushed out in the morning with English war cries only to change them to French ones once inside, allowing them to let French cavalry squadrons burst in and seize the town.
