If generals train to fight the last war, then security consultants train to foil the last terrorist attack. How else to explain the millions of dollars that are being spent in our cities to thwart truck bombers? Surrounding public buildings with a variety of obstacles has become the obsession of homeland security units nationwide. Following the attacks on the World Trade Center in 1993 and in Oklahoma City two years later, the authorities had to do something. (Or did they merely have to be seen to be doing something?) That something turned out to be "perimeter security": that is, stopping the putative truck bomber as far away from a building as possible. The New Jersey Median Barrier, invented in 1955, is designed to redirect a tractor-trailer going 60 mph, so it was a natural choice, or at least an expedient one. The problem is that huge hunks of reinforced concrete in city streets are not only an eyesore and an impediment to movement, they're a blatant and unsightly expression of a siege mentality.
The alternatives to Jersey barriers are concrete planters: security plus beautification. These days there are so many planters on the streets of Washington, D.C., that the city resembles a horticultural show. The rather fancy containers in front of the Reagan Building are full of red and white begonias, the tubs next to the Commerce Department have arrangements that look like large Mother's Day bouquets, while Justice favors giant sake cups filled with some sort of saw grass. There seem to be different theories of the best way to arrange these giant flowerpots. Treasury lines them up like parked cars, the FBI places them haphazardly in a picturesque arrangement, as if they were there by chance.
To meet crash ratings, planters have to be bulky and close together, which likewise clutters up sidewalks. The security industry, which, one suspects, drives a lot of these "solutions," has helpfully provided another alternative: the bollard. Bollards originated as heavy timber or stone mooring posts on docks, but as long ago as the Renaissance they were used to limit the passage of vehicles. When Bernini laid out St. Peter's Square in Rome, he designed beautiful granite bollards to keep carriages from driving into his fountains. Modern bollards are made of stainless steel, concrete, or stone wrapped around a crash-proof structural steel core. But even today's handsome security bollards have major drawbacks compared with Bernini's version. To resist a fast-moving heavy truck they have to be 36 inches tall—much too tall to sit on—and close together and no more than 4 feet apart. A row of security bollards marching down a sidewalk resembles a line of midget guards and is not much of an improvement over Jersey barriers.
Given our tendency to overreact and to cast blame—who wants to be accused of doing nothing after the next terrorist attack?—we appear destined to live with perimeter security for a long time to come. The best approach may be not to pretty it up but to make it disappear. The best current example surrounds the recently reopened Washington Monument. Several years ago, Congress mandated the National Park Service, which is responsible for the Mall, to secure the monument from truck-bomb attack, which required establishing a 400-foot security perimeter. Instead of deploying hundreds of security planters or bollards, the Olin Partnership, landscape architects, created the modern equivalent of a ha-ha, the hidden deer fence that was a common feature of 18th-century English estates. Olin's ha-ha is an unobtrusive retaining wall that follows the paths that curve their way up the hill to the monument plaza. The low granite wall makes a convenient place to sit and is nice to look at. (It recalls Frederick Law Olmsted's low garden walls at Capitol Hill.) That it also happens to be designed to stop a madman in a Hummer seems almost an afterthought.