Not a lot of historic landmarks in Vientiane remain in their original forms, having been numerous wars and invasions—particularly the Siamese onslaught of 1827 and the Indochina Wars that lasted for 55 years. A few exceptions are Wat Si Saket, a Buddhist temple built in 1818, and That Dam, an ancient stupa steeped in legend.

Standing in the center of a roundabout near the Talat Sao morning market, the stupa is believed to be around 500 years old, though the exact date of construction remains uncertain. The name That Dam (not that dam) means “black tower” in Lao, based on its current status. However, it was not always darkened and overrun with weeds; local legends claim that it was once gilded over and that the gold was all stripped away by the Siamese invaders.

Generally, stupas are built to enshrine Buddhist relics, most often the ashes of monks and nuns, sometimes of kings. In the case of That Dam, it is unknown what is buried inside, but locals whisper of an intriguing legend. According to them, lying dormant underneath the stupa is the Naga, a seven-headed serpent that will awaken whenever Vientiane faces a crisis. Many of them believe that it has protected the city from the 1827 invasion, as well as on other historical occasions.

The stupa has fallen into disrepair since the Naga last showed itself, weather-worn and all but neglected, but there are still believers in the powerful serpent. In fact, some locals seem to continue to visit the ancient monument to dedicate flowers to the forgotten guardian of Vientiane, in hopes that its peaceful slumber will never again be disturbed.