The Bayeux tapestry, a colourful ancient linen roughly the length of a Boeing 747, is back in England for the first time in around 950 years. Its run at the British Museum, opening September 10th, is heralded as a once-in-a-millennium show. Around 1m people are expected to see the tapestry in London while on loan from the French state, making it one of the best-attended museum exhibitions in British history.

Insured for £800m ($1.1bn) under a government indemnity scheme, its value parallels the $1.1bn inflation-adjusted worth of the Mona Lisa’s 1962-63 US tour. The tapestry depicts William the Bastard-turned-Conqueror’s triumph in the Norman conquest of 1066, likely commissioned by Bishop Odo of Bayeux to celebrate his half-brother William’s victory. Made probably in Canterbury in the 1070s-80s, it offers an intricate, sometimes wandering account of a broken promise and ascent to power that changed England’s royal line, class structure, and language.

The taperm ends mysteriously, with the final section missing—possibly ending at William’s coronation on Christmas Day. It contains 737 animals and 627 people, only three of whom are women in the main embroidery, alongside Latin phrases, Aesop’s fables in the margins, and bizarrely prominent genitalia. Historians like Benjamin Pohl of the University of Bristol note that questions about who stitched it, why, and its intended destination remain disputed, with ten historians potentially offering ten different answers.

A competition invites children to imagine and stitch a conclusion to the missing end.