If we want to find out what kind of technology people used in the past, we normally have to depend on archaeologists to find ruined(毁坏) buildings and parts of tools or instruments or machines. Archaeologists then try to reconstruct(修复),sometimes with the help of computer technology, what these ancient buildings and objects must have looked like, and how they might have been made. Sometimes historians are lucky and find an ancient document with a written description of these ancient buildings and objects.
We can understand, then, why Chinese historians were so excited when they found cave paintings which show ancient science. They found these paintings in the world-famous Mogao Grottoes of Dunhuang City, in Northwest China's Gansu Province. There are 500man-made caves with a history of at least 1,600 years. Almost all of these caves have paintings on their ceilings or walls and they date from the 4th to 14th centuries. Wang Jinyu is an expert on these cave paintings (also called frescoes(壁画)) and he says, "We discovered frescoes with scientific and technological content in almost all of the caves which have frescoes." According to the Xinhua News Agency, these cave paintings provide evidence(证据) of ""scientific and technological inventions by ancient Chinese in maths, physics, chemistry, geography, traffic and transportation, arms and military equipment, ...etc."
Among the discoveries that experts have made are cave paintings showing ancient techniques of pottery making and wine production as well as paintings showing ancient weaving machines and then toothbrushes! The paintings also give some evidence of the lifestyle at the time with, for example, pictures of people boiling milk over 1,000 years ago. Experts believe that there is more evidence to be found, but even now the caves are a wonderful natural museum. If the walls and ceilings of the caves were all put together, they would form a tapestry(壁毯), 20 kilometers long and 2 meters high!
It won't be possible to travel back in time—that only happens in films—but visiting these caves would be the nearest experience you could get to travelling back in time.
