As anyone who saw Merlin tonight would know, taking a castle involves burning torches, a traitor on the inside, lots of death and some bandits. However it doesn't have to be this way. As a small band of Welshmen proved in 1401, it can just be really, really sneaky instead.
At the beginning of the fifteenth century, the lands that make up modern day Wales were at war, with the Welsh leader Owain Glyn Dwr leading the fight against English control. Their fighting mostly consisted of skirmishes and raids, since the Welsh weren't foolish enough to engage the English in open warfare. However in 1401, a group of 40 or so of Glyn Dwr's supporters succeeded in something much more dramatic - they captured Conwy Castle, the enormous fortress built by King Edward I in the thirteenth century to subdue the natives in the surrounding region after his conquest of Wales.
It looks like this, by the way.
Not the most welcoming or accessible of places as you can see.
Naturally the chances of 40 or 50 people taking a heavily garrisoned castle in a walled town populated by a large number of loyal Englishmen were quite low. Which was why on April 1st 1401, the Welsh took advantage of the Good Friday celebrations to sneak their men into the town - some say disguised as carpenters - and then simply wait until the castle garrison marched out to attend the church service being held in St Mary's Church in the walled town.
As soon as the garrison left - leaving TWO PEOPLE to guard the castle (they really brought this on themselves) - the Welsh marched in and showed just how well designed and formidable Edward I's castles were by holding it for three months with only 50 men at arms under the command of William ab Tewdwr. When they finally gave it back to Henry Percy (Henry Hotspur) the Lord Justice of Chester and North Wales appointed by King Henry IV, they did so with terms favourable to themselves and not King Henry, who would later angrily repudiate the terms Hotspur had negotiated.