Six years ago in the spring, as COVID-19 cases grew in distant China, Britain was torn between sealing the country off and letting daily life continue its restless hum. For people who lived through it, those weeks — and the subsequent months — were a strange state of upheaval. Today, that collective experience is etched into London's landscape. Raised by ordinary citizens in 2021, the 1,640-foot-long National Covid Memorial Wall stretched along the bank of the River Thames, directly opposite the Parliament, as if holding vigil over the nation's corridors of power. On a recent visit, I took a walk...