As a ruler of the Qing empire, Emperor Qianlong (r. 1735–1796) not only loved to read but was also passionate about compiling books. If we were to name the largest book series in history, it would be the Complete Library of the Four Treasuries (Siku quanshu)—commissioned by Emperor Qianlong of the Qing dynasty (1644–1911).

You may have heard this book series title in period dramas and Emperor Qianlong commissioned the compilation of it. But what does “Four Treasuries” mean? This classification is rooted in China’s ancient system of organising books into four main categories: Classics (jing), Histories (shi), Masters (zi), and Belles-lettres (ji). “Classics” refer to the Confucian canon; “Histories” are official histories written by historiographers; “Masters” encompass writings of various schools of thought; and “Belles-lettres” are anthologies of poetry and literature.

Calling this the largest book series isn’t about its physical size but rather its vast content and sheer number of volumes. It encompasses over 3,500 significant works from the pre-Qin period (before 221 BCE) up to the Qianlong period of the Qing dynasty, covering all major achievements in literature, science, and technology. How large is it? The Complete Library of the Four Treasuries was bound into over 36,000 volumes, stored in more than 6,100 folding cases, with a total of over two million pages!

Emperor Qianlong was a formidable ruler. His reign—when the nation was stable and the people lived in peace—marked a peak in the prosperity of the Qing dynasty, a period known as the High Qing era (1683–1799). But he wanted to achieve even more—to surpass all previous emperors culturally. And what could better realise this ambition than the creation of an unprecedented, monumental book series?

To create such a work, the best versions of each text had to be sourced—the first step was to collect various books circulating across the country. Emperor Qianlong repeatedly ordered officials nationwide to search for literary works from previous dynasties and contemporary writings and send them to Beijing. To encourage this effort, he even established a reward system: officials who contributed more than 500 books received a set of the Complete Classics Collection of Ancient China (Gujin tushu jicheng), over 5,000 volumes; those who contributed over 100 books received the Rime Storehouse of Esteemed Phrases (Peiwen yunfu), a 95-volume set. For especially rare finds, Emperor Qianlong would personally inscribe a poem in gratitude—a gesture more thrilling to officials than a celebrity’s autograph today.

Of course, only distinguished figures could be entrusted with this imperial task. Among them was the renowned scholar Ji Xiaolan (1724–1805), one of the chief editors of the project. Altogether, 360 officials and scholars joined this ambitious endeavour under Emperor Qianlong’s guidance.

After years of painstaking effort by hundreds of scholars, the Complete Library of the Four Treasuries was finally completed. To ensure its preservation, Emperor Qianlong ordered seven hand-copied editions to be made and placed in different locations for safekeeping. Due to the immense cost, only a few copies were printed using movable types. Every handwritten volume underwent meticulous comparison with the original, followed by repeated proofreading, ensuring accuracy before the books were bound and presented.

Did you know? Copying and proofreading this work became the most time-consuming and labour-intensive task of the entire project, spanning 14 years and involving over 4,200 individuals—a monumental effort in Chinese history.

Of the seven copies, the first four were housed in the “Four Northern Libraries”: the Belvedere of Literary Profundity (Wenyuan ge) in the Forbidden City, the Belvedere of Literary Foundation (Wensu ge) in Shenyang, the Belvedere of Literary Flowing (Wenyuan ge) in the Old Summer Palace, and the Belvedere of Literary Delight (Wenjin ge) in the Chengde Mountain Resort. The remaining three copies were placed in the “Three Southern Libraries”: the Belvedere of Literary Convergence (Wenhui ge) of the Daguan Hall in Yangzhou, the Belvedere of Literary Clan (Wenzong ge) of the Jinshan Temple in Zhenjiang, and the Belvedere of Literary Magnificence (Wenlan ge) of the Shengyin Temple in Hangzhou. The Four Northern Libraries were strictly off-limits, while the Three Southern Libraries were open to local scholars for study and transcription. The original copy, also accessible for transcription, was stored in the Hanlin Academy.

However, paper is vulnerable to water and fire. After enduring the passage of time, only three original transcripts survive today: the Belvedere of Literary Profundity copy is preserved in Taiwan, the Belvedere of Literary Delight copy in the National Library of China, and the Belvedere of Literary Foundation copy in the Gansu Provincial Library. The Belvedere of Literary Magnificence copy lost two-thirds of its volumes during wartime but was eventually restored three times and remains complete in Hangzhou. Tragically, the Belvedere of Literary Flowing copy and its duplicate were destroyed in wars of aggression, while the copies of the Belvedere of Literary Clan and Belvedere of Literary Convergence were lost in civil conflicts, resulting in irreparable losses.