Eddie Redmayne made an incredible discovery while preparing for his role in Birdsong.
The My Week With Marilyn actor plays the lead on Abi Morgan's BBC One adaptation of Sebastian Faulks' First World War novel Birdsong, and was taken to the tunnels under the Somme in Northern France to research the role.
"We went down these tunnels which had just been rediscovered and crawled around on our hands and knees amongst chalk rubble," he said.
In one tunnel, they discovered a poem written in pencil on the chalk wall. "It must have been almost 100 years since it was last read," Eddie said.
"It was extraordinary and incredibly moving to read, especially knowing that although Sebastian's piece is fictional, it is based on truth."
Despite being set in France, much of the shoot took place in Budapest, where the production designer constructed intricate rabbit warren-like trenches from scratch.
"The landscape was very similar to what it would have been like and the other thing that made it come to life was the baking summer heat in Budapest," he said.
"You're in these huge, really warm woollen clothes and that's exactly what [the soldiers] had to deal with," he said.
"I couldn't get over the fact that on the day we filmed 'going over the top', I had to wear a tie and a pin, whilst also being equipped with a revolver, but that's what an officer would have worn."
:: Birdsong, which also stars Clemence Poesy, is a two-part adaptation starting on BBC One on Sunday, January 22.