In 221 BC, the Great Qin unified the world. Zhou Qi, an engineer from the 21st century, is reborn in a rundown blacksmith's shop in Xianyang, carrying a black box from a highly advanced civilization. The box holds technology centuries ahead of its time, but it also leaks Earth's coordinates into the cosmos. Starting from the smithy, he rebuilds the Great Qin war machine, forges a galactic defense line, and prepares to face visitors from the stars who will arrive 87 years later. With a furnace full of molten iron, he lights up the entire universe.
A very interesting, coherent and interesting science and technology story.