While working on my latest book, The Lost Castle Treasure, I realized that without a helpful visual aid, keeping track of a whole castle was going to be difficult. I actually had to design an entire castle—all three stories, including the basement (or dungeons), secret passages, spy nooks, royal apartments, barracks, stables, and so much more. This brought back memories of all the wonderful adventures I used to have in my very own castle when I was a boy.

Okay, I admit it was actually a cardboard box, but in my imagination it was a real castle. One of the games my friends and I would play as kids was similar to tag with one big difference—the cardboard box, or castle, was the safe zone. Once we made it to the castle we were safe and nobody could touch us. Even in my imagination I recognized the importance of a castle for protection.

In medieval times that was the sole reason for building large, heavily fortified castles—for protection from marauders or invaders. Keep in mind that this was before the advent of gunpowder and cannons, so well-built, well-provisioned castles could actually stave off intruders for months and even years. Modern castles (after the invention of gunpowder) became more of a status symbol than a protection.

In this week’s blog I thought I would share a little bit of what I learned about the walls of castles built in the second half of the Middle Ages that made them so effective in providing protection.

A castle could have one or more walls as its first line of defense. These walls were built around the entire castle and were called curtain walls. The inner curtain wall surrounded the main castle buildings (living quarters, etc.). Often a second curtain wall was built surrounding the inner curtain wall with a good amount of space between the two curtain walls, although this plan was sometimes changed to suit the terrain. The height and thickness of curtain walls varied anywhere from 7 to 30 feet in thickness and anywhere from 30 to 40 feet in height.

Castle walls had to be built strong and were made of stone. The builders would dig a trench until they reached bedrock and then began construction of the wall. If the topsoil was too deep to find bedrock the builders would fill the trench with crushed stone. Why go through all of that extra work? To provide additional protection in case of a prolonged siege.

When a castle was under siege, attackers might start tunneling underground toward the castle wall. Being underground protected them from any arrows the castle’s defenders might shoot at them. As they dug, they braced the tunnel with wooden props so it wouldn’t fall in on them. When the tunnel was right under the castle wall, they would fill the end of it with straw and hay and pig fat and set it on fire. The fire would burn through the wooden supports and the tunnel would cave in. As the tunnel under the castle wall collapsed, many times part of the castle wall would fall down too, and the attackers could storm the castle. This is where we get the word “undermine.”

You’ll also notice from the illustration that the inside of the wall was filled with debris—like stones, mortar, etc. Some castles with very thick walls had stairs and passages (maybe even secret ones) built inside the walls that led to other levels of the castle.

One other important point about castle walls is that there were no big windows opening to the outside of the curtain wall. Windows would make the castle vulnerable to attack so the only openings in the curtain walls were up high, beyond the reach of an attacker, and they were generally very narrow—just wide enough to allow archers to shoot through them. Of course, safely inside the curtain wall, it was not unusual for some of the castle buildings to have larger windows to let in light.

Next week I’ll be interviewing Bob Lawson about castles. Bob is the curator of Ferniehirst Castle, Scotland’s Frontier Fortress, and has written several books about the castle’s history. (http://www.clankerr.co.uk/)