Marathon Man

It's marathon season on London's stages. Less than a month after the Royal Shakespeare Company (RSC) raised the curtain on its epic cycle of Shakespeare's plays This England—The Histories at the Barbican, the same venue hosts a show that claims to be the longest play ever written. Tantalus, penned by RSC author and director John Barton, is a vast retread through the saga of the Trojan War. Divided into nine parts, Tantalus lasts all of 10 hours—long enough to convey the scale of the decade-long conflict it depicts. (Playgoers can see the play in three installments over consecutive weeknights, or instead...