The "Six Dynasties" is the name for the six successive governments whose capitals occupied the great city of Jiankang (modern Nanjing/Nanking). They were:
222-280 Kingdom of Wu in the Three Kingdoms period
317-420 Eastern Jin dynasty
420-479 Liu Song dynasty
479-502 Qi dynasty
502-557 Liang dynasty
557-589 Chen dynasty
The last four of these constituted the so-called "Southern Dynasties", which maintained a relatively traditional Chinese culture in the newly opening south, as against the "Northern Dynasties", which were mainly non-Chinese. The period of division ended with the establishment of the Sui and its defeat of the Chen in 589.
Although the Six Dynasties period was one of terrific political upheaval, it was also a time of great cultural ferment. There was much synthesis of foreign influences and native Chinese tradition, on a scale not seen in China until the 20th century. In many respects the language and culture of China as we know them today were cast during the Six Dynasties period. It is unfortunate that textbooks and histories often pay so much less attention to this period than to the Warring States or the Tang and Song.
A note on Nanjing: Note that Nanjing was also the first capital of the Ming dynasty, and of the Republic of China before it fled the mainland to Taiwan.
Nanjing means literally "southern capital". Historically it has been much more roundly a Chinese political and cultural center than Beijing. (Although Jicheng, the capital of the old Warring States state of Yan, was situated near modern Beijing, in imperial times Beijing was the capital mainly of non-Chinese dynasties, apart from the latter part of Ming. The state of Yan was, itself, weak and considered semi-barbarous.) The other great historical capitals of China have been Luoyang and Chang'an (now Xi'an). They were last important political centers during the Tang dynasty, which ended in the early 10th century C.E. Nanjing should be known as one of China's principal capital cities. | 
