The place where gunshots were reportedly fired Monday in the U.S. Capitol complex, the Capitol Visitor Center, actually came about to protect such attacks. The instigating incident came on a hot July day in 1998, when a gunman stormed past a security checkpoint and fatally shot two police officers on his way into the halls of power.

An armed assailant stormed past a U.S. Capitol security checkpoint, mortally wounding Officer Chestnut. In the initial crossfire between the gunman and Capitol Police, a gunshot injured a tourist. As congressional aides and Capitol visitors sought cover, the assailant ran toward a door that led to the suites of then-Majority Whip Tom DeLay of Texas. Detective Gibson, a member of DeLay’s security detail, told aides to seek cover. Gibson and the assailant exchanged gunfire. Although fatally wounded, Gibson’s action enabled other officers to subdue the gunman.

It was the first time a Capitol police officer had been killed in the line of duty. Within days of the attack, lawmakers started talking about reviving a stalled project to rebuild the visitor's center underneath the Capitol. It would be an air-conditioned welcome spot and meeting point for visitors, but Capitol police officers said it would also be a welcome addition to security by regulating the flow of visitors and providing an evacuation route in case of an emergency. Then-Senate Majority Leader Trent Lott (R-Miss.) said a center would have stopped the 1998 shooter from being able to get so close to the Capitol.

"The security checks would occur there, away from the building itself," Lott said at the time.

Social video shows panic inside Capitol Visitor Center (The Washington Post)

The idea of building a visitors center first sprang up a decade earlier, when a bomb went off in 1983 on the Senate side of the Capitol, ripping open the doors to the cloakroom where senators gather off the floor, reported The Post's Juliet Eilperin. In 1989, a camera crew followed a columnist as he breezed through security checkpoints with a pistol and a bullet.

Lawmakers debated whether to spend the hundreds of millions to build the visitor center until the 1998 shooting that seemed to galvanize support -- although not universally.

"It's not a cure-all," said Rep. James T. Walsh (R-N.Y.) at the time. "If there had been a visitors center, he probably would have killed someone in the visitors center. No matter where you stop an angry person with a gun, someone is going to get hurt."

Construction started on the center in June 2000, and it was finished eight years later, almost nine times more than originally planned. Today, the center is massive; it includes a theater, three auditoriums and the largest cafeteria in Washington, and it can hold up to 4,000 tourists.

There have been several threats of violence in or near the Capitol since then. In 2012, a man was arrested in a parking garage wearing a vest he thought contained explosives. It was a sting operation. In 2013, during a government shutdown, police shot and killed a woman after she drove her car into a White House security checkpoint and struck a Secret Service officer, then drove the short distance to the Capitol, where Capitol Police chased her down.

The most infamous incidents of violence in the Capitol occurred decades before the visitor center was conceived. In 1971, a protest group set off a bomb on the first floor of the Capitol, causing some $300,000 in damage but no injuries. In 1954, four Puerto Rican nationalists opened fire on the balcony overlooking the House of Representatives chamber, injuring five lawmakers. President Andrew Jackson survived an assassination attempt in the Capitol Rotunda in 1835.

Tourists visiting the U.S. Capitol in Washington, D.C. described a tense situation after shots were fired inside the Visitors Center. (Reuters)