Bollards are short poles or stands that serve many purposes: They are used to moor ships and as traffic markers, antiterrorist barriers, and street furniture upon which people can perch, lean, or sit.

After the terrorist attacks of September 11, 2001, bollards blossomed around the city and especially in Lower Manhattan, with bronze-colored blocks prohibiting vehicular entrance to Wall Street at Broadway, and thin black poles lining the sidewalk around various buildings, including 140 Broadway and 26 Federal Plaza.

The nicest bollards in the city are at the entrance to the office building at 11 Madison Ave., at the northwest corner of 24th Street, at the driveway entrance to the apartment building at 45 E. 89th St., and around the Park Avenue Synagogue on the southeast corner of Madison Avenue and 87th Street.

Less attractive bollards are ubiquitously (and mysteriously) placed next to fire hydrants and behind public telephone booths.

The newest bollard booty can be found in the meatpacking district, where six sections of Gansevoort Plaza on Ninth Avenue between 14th and Gansevoort streets have been demarcated by some orb-like bollards that have been referred to on the Internet as “bulbous breasts,” or “bon-bons with reflective tops,” as well as stacked and stepped blocks of concrete.

People often can be seen sitting on the concrete blocks in front of Pastis Restaurant, and on a recent day, a group of middle-age men were seated in the midst of the bollards on cloth chairs they had brought with them, as if to defy the oncoming tanks of urban planning. When questioned why they weren’t sitting on the bollards, one of them replied that the barriers were “too hard.”

Last December, the artist Daniel Buren created a controversy when he demanded that the French government dismantle “Les Deux Plateaux,” his famous 1986 installation of 260 bollards, all painted with black-and-white vertical stripes, in a large courtyard at the Palais Royale in Paris. Mr. Buren, who was given a major retrospective in 2005 at the Solomon R. Guggenheim Museum in New York, argued that the immensely popular installation, which included an underground level with lights and water channels, had not been properly maintained.

A few years ago, the artist Jan Mitchell created 104 very amusing bollards that sit along the waterfront in Geelong in Victoria, Australia. He painted lifeguards, women, and nuns on cut-down telephone and electricity poles, which are known locally as the Bay Walk Bollards.

Mr. Horsley is the editor of CityRealty.com.