In Son Tay Town, about 40km from Hanoi City, the Son Tay Cotadel was built of hard sandstone with one gate on each side. Son Tay Citadel was erected in 1822. The wall is surrounded by a 3m deep, 20m wide moat. Each corner of the citadel was armed with cannon. Furthermore, there is the Kinh Thien Palace – the rest house of the king, residences and offices of provincial leaders, warehouses, and troop camps. Due to time and the effects of war, parts of the ancient wall were destroyed. Measures to prevent and restore this historical relic have recently been implemented.