The first thing you need to know about this animated feature from China is that it is 168 minutes long, or two hours and 48 minutes. That’s a lot of time to spend watching a story about Chinese poet/warriors from the eighth century, celebrated via a screenplay that’s dense with historical incident drawn from the subjects’ biographies. If you know nothing about this period of history, which unfolds during the Tang dynasty, you’ll certainly learn a lot, but you’ll need to pay close attention to the welter of journeys to far-flung provinces, battles fought in mountain passes, and characters of note met along the way.

The two main characters are governor and general Gao Shi (voiced as a young man by Yang Tianxiang, as an elder by Wu Junquan) and poet Li Bai (Ling Zhenhe and then Xuan Xiaoming). The latter was considered one of the greatest poets in Chinese history, and the film honours him and his work by featuring dozens of his poems, often declaimed lustily by the character in various states of inebriation (he was a legendary drinker). Gao Shi was also a poet of some note apparently, but the film makes it clear he was not in Li Bai’s league. Instead, Gao Shi gets to basically narrate the story of his and Li Bai’s entwined lives in one long flashback, told to a visiting luminary over the course of a single night before a decisive battle. (Surely the storytelling could wait so that the elderly Gao Shi could have a good sleep before the fight?)

Chang’an, the title under which the film is released in the UK, refers to the ancient capital of China, of which we get to see quite a lot in the course of the story, rendered in gloriously intricate detail. The animation is indeed quite spectacular: fine grained as antique wood, made to be shown in 3D so that every pore and hair is practically photorealistic. No less care has been expended on the characters’ expressions, so the level of animated acting is very high indeed. That said, it all feels like a massive propaganda construction, celebrating a Chinese heritage that was maximally expansive and culturally significant, able to lord its sophistication over the barbarians at the borders. It’s significant, perhaps, that this subject should be chosen now, but if you want to appreciate an unquestionably impressive example of state-sponsored art, have a look at this.

• Chang’an is in UK and Irish cinemas from 28 February.