Thanh Hoá is a large province of Central Vietnam. Thanh Hoá is composed of three categories of mountain, plain and mid-land terrains. Its coastline is 102km in length. Being the dwelling place of the ancient Viets, Thanh Hoa is proud of the glorious Đông Sơn culture (see also Các Nền Văn Hoá ở Việt Nam). Only 16 km from Thanh Hoá City, Sầm Sơn Beach is very good for bathing. Beside sandy beaches, Sầm Sơn also has some scenic spots such as Trong Mai Island, Doc Cuoc Temple and Co Tien Mount. Citadel of the Hồ Dynasty (Thành Nhà Hồ) was built in 1397. It was not only the location for the central government, but also a quite military project. All the ancient citadels in Vietnam such as the citadels of Hoa Lư and Cổ Loa were made of earth, the only exception being the Hồ Dynasty Citadel, which was wholly built in block granite, depicting the power of creativeness and industriousness of the labouring people more than six centuries ago. The Hồ Citadel Dynasty only existed for 10 years (1397-1407), but its vestiges are still surprising because many of its technical questions remain the unknowns