The old London Bridge was an astonishing example of urban density, a form of peak urbanism centuries before the concept had a name. For hundreds of years, it was not merely a crossing but a fully inhabited, multi-story neighborhood. Houses, shops, and chapels lined both sides, packed so closely that the bridge functioned as a linear city. Hundreds of people lived above the Thames, sharing the narrow roadway with merchants, carts, and nonstop foot traffic. The result was a self-contained urban ecosystem where daily life, commerce, and infrastructure were tightly interwoven in a vertical, crowded metropolis. Over time, this medieval arrangement became unsustainable. By the 18th century, the aging buildings posed fire risks, blocked light and air, and severely hindered movement on both the bridge and the river below. Maintenance grew difficult, and the arches restricted navigation. In 1831, the structure was demolished and replaced slightly upstream by John Rennie’s granite London Bridge, designed for safety and efficient traffic rather than habitation. That bridge was later dismantled in the 1960s and rebuilt in Lake Havasu City, Arizona. While modern London bridges remain functional, none recapture the dense, lived-in vitality that once made the old London Bridge a remarkable experiment in city building.(Historic Vids)