Within the ancient city Muang Fa Daet Song Yang there are a 5 pagoda bases on a square plot aligned in a north/south direction while to the north the principal pagoda Prathat Yaku has been restored. Prathat Yaku, also known as That Yai Temple was built in the Dvaravati Period. Later in the Ayutthaya Period it was renovated with the addition of a stupa to an octagonal plan. Finally, the top part was added in 1932 by a team of Vietnamese artisans. Yaku is a word in northeastern Thai dialect as the name of revered Buddhist monks. The stupa is thus believed to have been used to carry the ashes of a significant monk. The Yaku Stupa is built of brick on a multi-leveled octagonal base with indented corners and lotus-petal shaped decorative figures. There were originally 11 boundary stones, locally called sema, placed in all eight directions around the pagoda. Some semas bear figures depicting the past life of the Buddha. The moats that surround the pagoda were constructed in 1983 for flood control. Prathat Yaku was registered as a national ancient monument in January 1937.