They were exposed to the great fortresses of the Holy Land, different architecture and advanced siege warfare tactics and siege engines. This new found knowledge and ideas helped to improve the designs of concentric castles making the task of defending a castle in Medieval Times easier.

Defending a Castle in Medieval Times - Siege Warfare
Successfully defending a castle during the Medieval times of the Middle Ages depended on whether the castle and its inhabitants could withstand a siege. Understanding Siege warfare was critical during the Medieval times and era. The concentric castles of the Middle Ages were designed with this in mind and included defence features such as the Moat, Portcullis, Barbican, Gatehouse, Crenellations and Drawbridge. 

Defending a Castle in Medieval Times - Withstanding a Siege situation
The site of a castle was chosen carefully. The following factors were considered:

• Castles were always built on land containing a well or a spring - so lack of water was not usually a problem. It was essential for the inhabitants of a castle to have access to a well
• Many castles were built with direct access to the sea, or a river, so that fresh supplies could be delivered to the castle and the defenders could not be starved into submission
• Water was also required to douse any fires within the castle complex
• The inhabitants of Castles which were built inland ran the risk of being starved into submission
• The higher the land the castle was built upon the easier it was for defending a castle

Defending a Castle in Medieval Times - A Defence strategy
A sound defence strategy was a vital requirement of the lords, nobles and knights defending a castle during the Medieval times and era. The central tower or keep was the most important building in a castle complex housing the family of the lord of the castle and his valuables. All buildings were expendable - the keep was the most highly defended building. The attackers had to get through a series of castle defences before reaching this inner sanctum of the castle. The Strengths and Advantages of Castles described illustrating the strategies applied when defending a castle during the Medieval times of the Middle Ages:

• Round - shaped Keeps or Towers were built eliminating the weak corners of the square keeps which were easy to undermine
• The concentric castles were massive allowing many soldiers to be housed in the castle complex
• Moats were surrounded the whole Concentric Castle complex
• Some moats were up to 30 feet deep
• Castle moats could be filled with wooden stakes or water
• Water was preferable - filling a moat with water reduced the risk of tunnelling and potential fires
• A solid, thick outer wall, called the curtain wall, surrounded the whole of the castle complex. A Curtain wall was built between 6 and 20 feet thick
• The Curtain wall, had projecting towers to house soldiers defending the castle
• Various other walls within the castle complex were built at different levels - the highest wall being the Inner wall - this allowed the defenders of the keep or tower to have a clear view of any attackers
• The main entrance to the castle was the castle gate, or gateway
• Considerable engineering skills were put into strengthening and reinforcing the gateway which was the weakest part of the Castle. The main entrance, would be heavily barred. A series of entrances further aided those defending a castle
• Castles with a moat required a drawbridge. The drawbridge consisted of a wooden platform with one hinged side fixed to the castle wall and the other side raised by rope or chains. The purpose of a drawbridge was to hinder or prevent fast and easy entry into a castle
• The Portcullis was a heavy grilled door that was suspended from the Barbican or gatehouse ceiling. The portcullis was meant to be lowered quickly in times of attack. Ropes could be quickly slashed or a fast release catch was enabled. The portcullis would come crashing down blocking the entrance to the castle, the spikes impaling the enemy soldier
• The Barbican was an exterior castle defence situated at the entrance of the castle which confined the enemy soldiers in a narrow passage. The Barbican was an exterior walled passage with multiple gates leading to the main entrance ( the Gatehouse)
• The Castle Gatehouse was a fortified structure built over the gateway to a castle
• The Barbican passage contained Murder Holes in the ceiling and arrow slits on either side of the barbican passage. The barbican is also referred to as the Death Trap
• Murder Holes were holes in the ceilings of castle gateways, barbicans or passageways through which heavy missiles or dangerous substances could be thrown on the enemy when defending a castle during the Medieval times and era. The Missiles dropped from 'Murder Holes' included heavy stones, hot sand, molten lead, boiling water and boiling tar or pitch
• A castle Battlement was a rampart built around the top of a castle with regular gaps for firing arrows. The parts called the Crenels was the 2-3 feet wide gap and the Merlons were the solid portion between two crenels. Battlements are also called crenellations
• Machicolations were projecting parapets or platforms situated at the top of a castle wall, some spanned the whole of the battlements whilst other Machicolations protruded from the walls like balconies
  • The purpose of the full Machicolations was to provide clear access across the top of the battlements enabling the soldiers to quickly follow the attack point of the enemy
  • The balcony style Machicolations had holes in the floor for dropping various missiles on the enemy which were called Murder Holes
• Castle Loopholes were narrow vertical windows from which defenders launched their arrows from a sheltered position
  • Castle Loopholes were accessed from wide inside areas narrowing to long, narrow apertures
  • Loopholes were different designs and sizes which accommodated the shape of different weapons such as the bow which was launched vertically or the crossbow which was launched horizontally
• The Castle Bastion was a small tower, which was situated at the corners, the middle or at the end of the curtain wall. The purpose of a Bastion was to cover any 'blind spots' in the castle curtain wall

Defending a Castle in Medieval Times
The defenders would use all the traps which were built into the castle designs to their best advantage when defending a castle in Medieval Times. The siege engines which mounted heavy attacks on a castle would be attacked using fire and grappling irons. Defenders would maintain a constant assault on the enemy by firing arrows, stones and crossbow bolts. Defenders launched arrows from the sheltered windows called loopholes.