This year marks the 600th anniversary of the completion of Beijing’s Forbidden City. For the first 500 of those years, the complex was the center of imperial rule in China, the seat of 24 emperors, and the home of a vast collection of artwork, relics, and artifacts amassed by successive royal families over centuries — over 1.5 million items in total.

Then the collapse of the Qing dynasty in 1912 thrust the erstwhile palace into a new role: a museum and repository for the cultural heritage of a new Chinese nation. Before staff of the newly christened Palace Museum had even finished cataloguing the collection, however, they found themselves faced with an existential threat, as Japanese encroachments into Chinese territory in the 1930s made the collection’s continued presence in Beijing untenable.

What followed was a nearly 20-year-long odyssey across China — and for at least part of the collection, around the world. From Beijing to Shanghai, on to London, then back to Shanghai and deep into the country’s mountainous interior, Palace Museum staff shepherded China’s most valuable relics through everything from political power plays to Japanese air raids. In their care was more than just a few scrolls of calligraphy or pieces of pottery; it was the spiritual heart of the nation. And in 1947, when the collection was finally, albeit briefly reunited, they prided themselves on the fact that not a single piece had been damaged, not a relic lost.