Bostonians, of which I was one for many years, come to gawk at the sudden shamelessness of the flowering, so at odds with the city’s customary inwardness and severity. Spring here is meant to be a gift as lavish as the winter is brutal. Until now, the usual threat to this outburst of April happiness has been the odd freak storm landing globs of clotted snow on the daffodils, breaking the necks of their stalks and the hearts of us gardeners.

But the spring reawakening is also an act of history. Patriots’ Day, celebrated only in Massachusetts, and the day the murderers chose for their atrocious gratification, commemorates the beginning of American liberty, when on April 19 1775 on Lexington Green British redcoats in search of secret arms caches ran into a citizens’ militia determined to stop them. In a chaotic exchange of fire, eight of the Lexington Minutemen were killed. There was blood shed on that morning, too, but unlike whatever demented motives might have led to the Boylston bombings, Lexington’s blood was spilled in reluctant desperation and as an act of resistance to coercion.

For years we lived in Lexington, and my wife and I would take the children to see the re-enactment of the battle before dawn, brimming with mixed loyalties but exhilarated by the drama that made history echo with the crack of muskets. It was high-class reconstruction, impeccable to the last detail of uniform, with British regulars looming out of the darkness to a steady drum beat, their major barking out the command to the “damned rebels” to lay down their arms; the volley and the return snap of musket fire; a general flight of the surviving Minutemen. Then, as light came up, we all trooped off for the fried dough that owed more to Boston’s Italian history than to 1775.

People thronged to Lexington from professorial Cambridge; from patrician Back Bay; from sylvan Lincoln and Wellesley, and from the gritty, “triple-decker” apartment blocks of Everett and Medford. Brit or Patriot, ferociously Irish (Noraid collection boxes could still be seen in the early 1980s in newsagents in Charlestown) or gently Armenian, we were all there, linked in a communion of memory; explaining to our kids what had been at stake all those centuries before; why it still mattered, why it was about something that changed the world.

The mutilations of Patriots’ Day 2013 were enacted in mindless cruelty, not mindful remembrance, and will change nothing; not even, one hopes, the public’s state of mind at all the sporting events that constitute the city’s true calendar of devotion, with Fenway Park, where the Red Sox baseball team play, its cathedral of light.

Above all, the futile atrocity will not damage Boston’s sense of itself as a city that refuses to be flattened into a generic version of urbanism, with the same malls, multiplexes and multistorey car parks controlling the rhythms of city life.

To be sure, all those things exist in Boston but so does the sense of a chain of urban villages; each distinct in their own way, some of them beautifully connected by Frederick Law Olmsted’s “emerald necklace” of parks and public gardens. South Boston is still hardcore Irish, facing the water; South End’s bow fronts forever in states of gentrification; cobblestoned Beacon Hill, built by land speculators in the earliest years of the Republic, where we lived for a while right below the golden domed State House, one of the most perfect expressions of residential neighbourhood ever designed.

And overlooking the bloodstained sidewalk is a place representing everything the murderers hate: civility, tolerance, enlightenment: Boston Public Library. Originally created in 1848 as America’s first free municipal library, it was rebuilt on its present site by the great Charles McKim in the 1890s. Go up the grand staircase and you will find the unfinished grandiloquent murals of John Singer Sargent, which he called “The Triumph of Religion”.

But Sargent’s title is misleading for he meant his painting to be not a statement of dogma but its opposite – the triumph, in fact, of toleration; of the absolute privacy of moral convictions, a credo that linked the Virginian, Thomas Jefferson, with the Massachusetts sage, John Adams.

Visibly moved at an interfaith ceremony in the city yesterday, President Barack Obama said the guilty would face justice. But perhaps whatever sentence is imposed on those who caused such suffering ought to include an obligation to march them up the library staircase and confront them with that imperishable American and universal truth: that a person’s beliefs are nobody’s business but their own. Heck, I’ll volunteer to do it myself.