One of the earliest documented sites in Nanjing, this former foundry and soldier training ground during the Spring and Autumn Period (722-481 B.C.) was a temple used by the Hongwu emperor (1382-98) as a ceremonial place of worship, hence Chaotian or "heaven-worshiping." The place was rebuilt in the Qing dynasty as a Confucian temple and academy. Today, the main hall, Dacheng Dian, houses a fascinating Six Dynasties museum. Exhibits include a locally unearthed Roman glass, a compass vehicle, and immortality pills, which obviously didn't work. The English explanations are quite good. Outside of the temple, an antiques market sells jade knickknacks and Mao posters.