Papermaking is refined by the Chinese eunuch Cai Lun, who receives official praise from the emperor for his methods of making paper from
tree bark, hemp, remnant rags and fish nets. Paper had been made in China from the 2nd century BC, but Cai Lun's paper provides a writing surface far superior to pure silk and is much less costly to produce. Bamboo and wooden slips will remain the usual materials for books and scrolls in most of the world for another 200 years, and paper will remain a Chinese secret for 500 years.
The Trajan Bridge is finished. For more than a thousand years, it is the longest arch bridge in the world to have been built, in terms of both total and span length.