 A seal script evolved further over the centuries, the top horizontal line became longer as is seen in Ban Liang cash coins produced during the Han dynasty.Emperor Qin Shi Huang conquered the various "warring states" and unified China in the year 221 BC forming the Qin dynasty.In order to consolidate central power of the new Qin dynasty, Qin Shi Huang proceeded to standardise the various scripts, weights, and measures that existed among the various states.