In 1672, the Worshipful Company of Spectacle Makers smashed 264 defective spectacles against London Stone with a hammer, a peculiar act of quality control that captures something essential about this battered block of limestone: nobody quite knows what it is, but Londoners have always treated it as important.

The stone has occupied Cannon Street since at least the 12th century, though its origins remain gloriously uncertain. Some historians suggest it marked the centre of a Roman governor's palace; others propose it was King Alfred's ground zero for rebuilding the city in 886.

The legend that mattered most to medieval Londoners held that while the Stone of Brutus stands safe, London shall flourish. In 1450, rebel leader Jack Cade struck the stone with his sword to claim lordship of London. It didn't end well for Jack, but the stone endured.

VoiceMap's self-guided audio tours trace such moments of medieval drama through the City's streets, revealing how this unassuming fragment behind glass at 111 Cannon Street became London's unlikely talisman.