That Dam, also known as the Black Stupa, is a 16th-century Buddhist stupa located on a tranquil roundabout in central Vientiane, near Talat Sao (the morning market) and the American Embassy. According to local legend, the stupa was once protected by a seven-headed water serpent, or Naga, and was covered in pure gold. However, during the Siamese-Laotian War in the late 1820s, the gold was looted and taken to Siam (modern-day Thailand), leaving behind the dark, weathered structure seen today.