Great Wall

Great Wall is a man-made barrier that protects the eastern borders of the Roble Holy Kingdom.

Background
It was built to withstand invasions from the massed demi-human tribes which occupied the hills to the east of the Holy Kingdom, between them and the Slane Theocracy. In order to keep it operating at full capacity, they had to keep a great deal of manpower permanently on site.

However, despite all of these defensive measures, the Holy Kingdom still remains vigilant of the constant danger and it still suffers from attacks from time to time. The gravest of these invasions came during the period known as the "Long Rain". It was a type of night attack instigated by a race called the Srush who were able to scale the wall and head deep into Holy Kingdom's territory. In the end, the Srush were driven back, though at the loss of several of the Holy Kingdom's villages.

While the wall may be massive to humans, it is no obstacle to races who are several times their size, can fly or possess some sort of special ability. This caused the Holy Kingdom's nobles to grow paranoid, resulting in the passing of a law to conscript all citizens. Once a citizen of the Holy Kingdom comes of age, they will undergo military training with the purpose of protecting their nation should it ever become necessary.

The Paladin of the Holy Kingdom Arc
Demiurge, under his Jaldabaoth guise, conquered and enslaved the entire demi-human population of the Abelion Hills. He then forced all those who were combat-ready into a huge allied army and attacked one of the fortresses at the Holy Kingdom's Great Wall. After Jaldabaoth single-handedly destroyed the fortress along with a section of the wall, he ordered his army to finish off any surviving soldiers.

Layout
The Great Wall is an 100 kilometer long barrier that safeguards the human kingdom from the dangers of the Wilderness and the vicious demi-human tribes.

There are only three gates along the entire length of the wall, which are heavily fortified. These fortresses also function as garrisons as well as staging areas should the demi-hunans invade.

Although they wanted to fully man the wall in order to prevent an event like the Long Rain from ever happening again, stationing troops at every single point along its length would strain the nation. Instead, they came up with a viable solution which was to build outposts at fixed intervals along the walls. These strong-points would then be overseen by gigantic fortresses. They stationed a small number of troops in these bases, their purpose being to fight for extended periods, to the last man.

If they managed to encounter an enemy attack however, they would first launch flares to request reinforcements. In addition, there were companies of soldiers who would staff and patrol the fortresses, serving as reserve troops during emergencies, to be deployed as the situation required. After putting these measures into practice, the demi-humans weren't able to penetrate the wall again for now.

The Holy Kingdom's defensive lines was made up of three walls linked altogether. There were only three fortified gates along the full length of the wall, which was in excess of one hundred kilometers long, and they also functioned as garrisons to dispatch troops to the surrounding strong points. If the demi-humans invaded and an overall mobilization order was given, they would become staging areas where the troops would gather in order to attack the enemy.

Trivia

 * The Great Wall here could be a reference to the Great Wall of China, built to keep out the Huns.
 * The Great Wall was supposedly built by the Holy Kingdom financially and through labor by their citizens.
 * According to the Holy Kingdom's history, upon the construction of the Great Wall finally being completed, an invasion by demi-humans ensued right afterwards.