Bollards are too much with us, but they just keep coming.

They march on Washington’s lovely landscape, one by one. Who even knew what a bollard was a dozen years ago? They are the best symbol for what ails us Americans in the 21st century — which, in my view, has pretty much been a flop so far.

After Sept. 11, 2001, green, gray and black steel posts sprang up on our sidewalks. Three feet tall, they stand in militaristic lines outside government buildings, often near street curbs, to deter car bombers.

Boston, Baltimore and San Francisco, similar cities to the District, put up bollards by some public architecture, but not in such overwhelming numbers, and the security posts don’t rule. In the District, seat of the federal government and national cultural treasures, they are the answer to everything.

The advance came with no public process, or apparent restraint, and it can be counted as a liberty we lost after the terrorist attacks. We lost the right to walk around our most meaningful outdoor places like free people, without bumping into a bollard. Hundreds of them stand sentry “guarding” the Capitol grounds, the White House, the Supreme Court, you name it. Washington National Cathedral and Union Station, spectacular gathering spaces of the same vintage, also sport them.

We pay a price for bollards that no doubt runs well into the millions of dollars, but I’m not talking about that. How much they aid public safety is up in the air. They wouldn’t prevent another air attack. That’s not really the problem, either.

Bollards separate our stately structures, scenic surroundings and majestic memorials. These are not just flaws in once-seamless sightlines. They are insults to democracy, you and me. Call them un-American for helping to change us into strangers to one another. They encourage everyone to be afraid, suspicious and closed to others passing by. They create a suggestion of danger that’s not worth it at the end of the day. Why let the likes of Mohamed Atta take trust and optimism away from us?

Look at the landscape design of the Capitol gardens and grounds, created by the masterful Frederick Law Olmsted after the Civil War. He envisioned the approach to the dome of democracy as flowing, transparent and open to all. Just as the dialogue of democracy represents all comers as equals in the public square.

Olmsted, the famous Central Park landscape architect, put the terrace and stairs on the West Front of the Capitol to fuse it with its setting. That also expanded the Capitol’s access in an elegant exterior form. Verandas always make a house or building seem more smiling and friendly.

In other words, Olmsted’s message spoke: “Come in! You are part of this place.” The opposite is true now. The bollards don’t beckon and invite you in — as a citizen — to witness the noisy marketplace of ideas and enjoy the grandeur of the Capitol Rotunda art.

Rather, they say: “Keep out!” Along with stumpy bollards, the Capitol police’s heavy presence — backed up by guardhouses and a hazardous material rescue truck — darkens the everyday experience. The Olm­sted plan’s lawns and trees have notably diminished since Sept. 11.

The northeast corner of First and Constitution avenues, on the Senate side, used to be an inspiring vista to the Capitol. Now it feels like the edge of a fortress. Nearby, the Supreme Court looks even worse. Bollards clash with the bright white marble stairs to the courthouse door, which is no longer a public entrance.

Then there’s the Treasury and the White House on Pennsylvania Avenue, which is closed off to traffic, with bollards working overtime. Such a wide-open street is not as ideal as it seems for creating civic order. On a sunny spring afternoon, about 25 Marines (off-duty) were doing a grueling “Goruck challenge” wearing camouflage. This required one guy to carry another on his back while sweating, grunting and swearing in view of the Treasury statues and tourists.

Little by little, bollards are coarsening our conduct, and soon schoolchildren won’t know America any other way. In the wake of the Boston Marathon bombs, it’s clear that bollards would not have stopped the Tsarnaev brothers. As Boston amply demonstrated, the best preparedness comes from quick thinking and coordinated actions by civilians, police, fire and medical personnel.

Washington, meanwhile, may be lulled into a false sense of security with our unsightly bollards.

Jamie Stiehm is a Creators Syndicate columnist.