The Han Dynasty (206 BCE to 220 CE) was the dynasty under which China reached its peak. After the Han state took over in 206 BCE following the fall of the Qin, the nation started to rapidly improve for the better. They took on a more peaceful form of ruling, Confucianism, that was much better than Qin Shihuangdi's Legalism. This ruling style would become the dominant law code in China for over 2000 years. The Han also drastically improved infrastructure, creating much better roads, buildings, etc.; this led to a much more technologically advanced and smoother running society. During the Han Dynasty, the Great Wall of China, one of the world's architectural masterpieces, was significantly improved on by the Han. Even though Shihuangdi started building the wall to keep nomadic invaders out, the Han made significant improvements to the wall, such as adding many more sections and repairing the already built ones. The Han was about as large as the Roman Empire, as they both ruled over around 50 million people and encompassed about one and a half million square miles. The Han Dynasty, through its various actions such as infrastructure improvements and ruling with Confucianism, changed China's history forever.

Han Chinese Territory at its Peak:

Staryer p. 160

http://en.wikipedia.org/wiki/Han_dynasty