The Mareten Wall is a staggering feat of engineering. During the Second Age, the Seer-King Brennus Aedan began it as his life's work - his life, and the lives of his children. From the First Age, the mountains reached past Wallace to the edge of the forest itself, where they continued as a long ridge of craggy foothills, through Annhoradwy Woods, all the way to the mountains in the south, against the sea. Under the direction of King Brennus, countless laborers carved stone from the mountains and moved it to fill gaps in the hills. At its conclusion, the wall was 25 feet tall and 100 feet thick, made of solid stone carved from the mountains. Earth was dug away to lay the stones on bedrock, and each stone was crafted to fit seamlessly against the others. Though the first wall was completed in his lifetime, King Brennus knew it would not be enough to stop the coming cataclysm. On his deathbed, he begged his children to strengthen the wall.
They did so; while his eldest son, Robert, ruled his kingdom, the twins Dafydd and Jonydd became the greatest builders in history. They built the wall straight and true, raising the height to 100 feet tall, and clearing the ground in front and behind. They began a second wall, a mile from the first. Originally, it was to be a second line of defense, and a secure road, but as the brothers observed the earth between the walls stamped flat by countless feet, they realized the gap could be filled entirely with earth, making a wall of immense thickness and strength. They ordered every cracked stone, every grain of sand chipped from the mountains to be dumped in the gap between the walls. The earth that had been dug away was replaced, filling the gap.
Though the two walls were finished well within their lifetimes, the brothers were not satisfied. They ordered the northern mountains reduced in height to 100 feet, and in width to a mile, to match the height and width of the wall; every last stone was brought by wagon and poured, layer after layer, into the wall. The stones were layered with earth and with magic, a gift from the descendants of the True Elves, sheltered in the kingdom. Though Dafydd or Jonydd could have become kings at the death of their eldest brother, they refused; their younger sister became queen, and then her eldest son, but the brothers toiled on.
Some said the strengthening magic of the Elves prolonged their lives; whatever the case, the two brothers remained alive far beyond their years. They were present at the final ceremony: the last wagon of stone was poured out, and the armies of the Wall marched over the stones to drive them in place. The stones locked together, but for two small rectangles that refused to settle. Irritated and embarrassed, the foreman turned to the two brothers, only to realize that they had died peacefully on their seats, their lifelong task complete. The King - their grand-nephew - ordered the two rectangles dug up, and the brothers buried there, in the center of Wallend. As the stones were replaced, they locked together into a single sheet of stone; a gentle rumble was felt through the entire wall as stone after stone clicked into place. As the wave reached the Tower, the stones snapped into place around it, sealing the tower to the wall. As the last stone fell into place, the tower shuddered, and a blast of magical energy poured through the wall. The perfect construction had joined Wall to Tower; the tower was opened, and the Wall was reinforced. The Wall was finally, and permanently, complete.
Less than a year later, the beastmen began to attack; while many descended from the mountains or rose up from the forest, the armies of Mareten were able to overwhelm them, destroying every last orc, goblin, ogre, and invading beastmen in the land. Though the age of man had come to an end, the vision of Brennus and the handiwork of Dafydd and Jonydd protected the realm, guaranteeing that the descendants of Man and Elf would live in safety.