Besieging a castle was a far more common form of warfare than a fight on an open battlefield.  Sieges had the element of surprise and required fewer men than battle too, such that a ruler could beseige a castle with his enemy inside, while freeing other forces to wage war elsewhere.

The goal in beseiging a castle was not to destroy it, but to take it, since castles were pawns in the great game of controlling land.  They were usually heavily fortified and defended, so a beseiger had several options when he was on the outside looking in:

1)  to starve/wait them out

2)  harassment and trickery

3)  a straight assault

Often, attackers employed all three tactics at various times.  The defenders, on the other hand, hoped and prayed for relief.  As Saladin says in Kingdom of Heaven “One cannot maintain a seige with the enemy behind”.  The hope was that a beseiged castle would be rescued by allies, and if they’d had warning of the seige, would have sent messengers out of the castle before their enemy closed in around them.

Castles in Wales that were beseiged:

Dolforwyn:  “Dolforwyn stands on a wooded hill overlooking the fertile Severn valley, a scene so peaceful today that it is hard to picture it as one of political animosity or military action. It was built between 1273-77 by Llywelyn the Last as a forward position in his territory, and overlooking the English lordship of Montgomery. This rectangular castle crowns a ridge along the Severn valley, and was obviously designed to act as a sentinel over Llywelyn’s south-eastern frontier. Its initial construction led Edward I to write to Prince Llywelyn in 1273, forbidding him to build the castle. The prince replied, with a masterpiece of ironic politeness, that he did not require the king’s permission to raise a stronghold in his own principality. Dolforwyn was, however, taken by Roger Mortimer after a fortnight’s siege in 1277.”

Hawarden:  “Hawarden’s most significant role in the struggle for Welsh independence came in 1282 when it was attacked by Llywelyn’s brother Dafydd ap Gruffydd. Angered by King Edward’s seeming lack of respect, Dafydd staged a night siege on the stronghold in the month of March [Palm Sunday]. Although he succeeded in capturing the castle and its constable, Roger Clifford, Dafydd’s actions forced his brother Llywelyn to become involved in another rebellion against the crown. By the end of the year Llywelyn had been killed, and Dafydd was on the run, only to be captured and executed the following year. Hawarden Castle was retaken by the English king, never again to be the target of a Welsh uprising.”

Harlech:  “Harlech Castle played a key role in the national uprising led by Owain Glyndwr. After a long siege, it fell to his forces in 1404. The castle became Glyndwr’s residence and headquarters, and one of the two places to which he is believed to have summoned parliaments of his supporters. It was only after a further long siege in 1408 that Harlech was retaken by English forces under Harry of Monmouth, later Henry V.

Sixty years later, during the War of the Roses, the castle was held for the Lancastrians until taken by Lord Herbert of Raglan for the Yorkist side. It was this prolonged siege which traditionally gave rise to the song Men of Harlech.”  http://www.youtube.com/watch?v=hz9_ELpil9w

Helpful links:

http://www.castles-of-britain.com/castlest.htm

http://www.deremilitari.org/resources/articles/bachrach1.htm

The Medieval Siege”  by Jim Bradbury

And because no post on medieval sieges is complete without it . . . I give you my son’s trebuchet: