The wrought-iron fence that surrounds the White House hasn’t changed since 1965, but that may be about to change after a Texas man jumped over it on Sept. 19 and made it all the way through the mansion’s unlocked door. (Nikki Kahn/The Washington Post)

The fence itself is 7 feet 6 inches tall. It is made of evenly spaced iron bars, mounted in a Virginia sandstone base. At the top of the bars — the last physical obstacle between the public sidewalk and the knob on the White House door — are little spear points, called finials.

Over the last 49 years, a lot of things have changed on the north side of the White House compound. Outside the grounds, the street is studded with car-stopping bollards, the result of 1980s fears about truck bombs. Pennsylvania Avenue — once a busy, honking commuter route — is quiet and empty, closed after the 1995 Oklahoma City bombing. Inside, special teams are deployed to send attack dogs after intruders who make it to the lawn.

What hasn’t changed is the fence between them.

It has looked the same since the Lyndon B. Johnson administration, when the government largely replaced a 19th-century iron fence with a new one that was at least eight inches taller.

“We haven’t done any other work since 1965,” said Jenny Anzelmo-Sarles, a spokeswoman for the National Park Service, which owns the fence (the White House is technically located in a national park).

Sightseers in Washington, D.C., react to new security measures put in place after Omar J. Gonzalez jumped the White House fence Friday and sparked a security alert. (Zoeann Murphy/The Washington Post)

And Anzelmo-Sarles said the Park Service couldn’t remember anyone — the Secret Service, the White House, anyone — asking for the fence to be changed. In fact, the Park Service is in the middle of a project that will repaint the old fence and remove the rust, without changing anything else.

“There’s no sort of tension or anything like that in recent memory” over the design of the fence, she said.

That may be about to change. Friday’s stunning intrusion at the White House — in which a Texas man made it over the fence, across the lawn and through the mansion’s unlocked door — revealed key failings in the Secret Service’s second line of defense.

On Monday night, the sidewalk in front of the North Lawn was lined with a series of metal crowd-control barriers, about waist-high and linked to run parallel to the White House fence for about 400 feet. Witnesses said at least some of the barriers were put in place on Monday night.

It was not clear whether they had been placed as a second line of defense against fence jumpers or in preparation for restoration work on the original fence, some of which is already underway.

Friday’s breach has focused new attention on the wrought-iron first line.

A spokesman for the Secret Service, reached by phone late Monday afternoon, said he was not sure whether the agency had requested changes to the fence and would not be able to answer the question without more research.

On Feb. 5, 1979, an early-arriving farmer leaves his tractor parked in front of the White House. The Secret Service is looking in to boosting security after an embarrassing security breach in which an intruder with a knife scaled the White House fence, dashed across the lawn and made it inside. (Jeff Taylor/AP)

The White House fence has changed greatly from its origins as a barrier for wandering livestock. But it had managed to remain a symbol of wary openness: a vestige of the old American idea that the president’s house was just a house, not a walled-off castle.

“I think there was an assumption that any intruder scaling the fence would be met with overwhelming force, immediately. That’s obviously not the case,” said Rep. Jason Chaffetz (R-Utah), chairman of a House oversight subcommittee on national security.

That realization, Chaffetz said, has made him interested in suggestions to change the fence itself. He said that, in past years, he heard suggestions about adding barbed wire, or bending back the iron bars at the top. But Chaffetz said none of those ideas ever made it far enough to be formally proposed to Congress.

“There are probably things that you could do to the top of the fence — without further impeding the public’s view of the White House — that would slow a would-be terrorist down or make it more difficult” to get over, Chaffetz said.

The first White House fence was erected by Thomas Jefferson in 1808. It consisted of wooden split-rail barriers on three sides of the grounds and a retaining wall called a “ha-ha” on the other side, where the South Lawn then bordered the Potomac River wetlands.

“It was to keep livestock from coming into the area around the house. It was not meant to keep people out,” said William Bushong, the chief historian at the White House Historical Association.

Over the next century, the old fences were eventually replaced with wrought-iron. But Bushong said the new fence was mainly for decoration, not for defense. In fact, the White House gates were left open much of the time, and members of the public could stroll in to visit the gardens or to wait for an appointment in the president’s waiting room. In 1842, an intoxicated painter got close enough to President John Tyler to hurl rocks at him. He missed.

The openness of the White House grounds began to change for good after an incident in the late 1890s. Bushong said that President Grover Cleveland’s daughter Ruth was with her nanny on the South Lawn when they were surprised by a group of people who had wandered in the open gates.

“A group of visiting women picked up Ruth and began to coddle her and kiss her and pass her around, and this really freaked out Mrs. Cleveland,” Bushong said. The grounds were closed, and the fence became a tool to keep people out. “The whole nature of the house and grounds as a public space really closed in the 1890s.”

In the 20th century, the remaining gaps in the fence began to close. The White House driveways were closed during World War II. The two small streets that ran through the White House grounds — East and West Executive avenues — were shut to traffic. The gates that closed these entrances were reinforced enough to withstand a high-speed ramming, and then protected by concrete barriers and bollards.

But, even as the White House became more of a fortress, presidents sought to make sure it did not look like one. In the early days of World War II, for instance, the Secret Service proposed to ring the White House with a new kind of fence: a wall of sandbags 15 feet high.

President Franklin D. Roosevelt said no. He kept the wrought-iron fence but stationed new guards around it.

“That’s all you need,” Roosevelt said, according to historian William Seales, who recorded the incident in his book “The President’s House: A History.” “As long as you have one about every hundred feet around the fence, that’s all.”

Martin Weil contributed to this report.