What's the name of Wang Xizhi's pile of hills?

Wang Xizhi built a hill called Pen Mountain. When Wang Xizhi was young, he practiced calligraphy very hard. It is said that he practiced calligraphy with a broken brush and piled it into a hill, which people called "Pen Mountain". There is a small swimming pool next to his home. He often washes brushes and inkstones in this pool. Later, the water in the small pool turned black, so people called this small pool "Mo Chi".

Wang Xizhi likes calligraphy since he was a child. After decades of hard work, his calligraphy art has finally reached the peak of transcendence and is known as the "book saint". When Wang Xizhi 13 years old, he happened to find that his father had a calligraphy book of Shuo, and he stole it. His father worried that he was too young to keep the secret of the family heirloom and promised that he would teach when he grew up.