I think it should be the prosperous social economy and culture.

The dynasty is supposed to be the high point of literature, the majority of most famous Chinese poems were composed during this dynasty. It is also the dynasty that used poem composition as a method of examination for office. Officials and the upper class were expected to write and draw in their spare time so the arts flourished.
It's also known as a golden age for women, because women enjoyed a relative amount of freedom and power, during the later dynasties their rights decreased severely.

maybe their famous because they invented gunpowder ang the magnetic compass