WASHINGTON (AP) — African-American slaves sweated in the summer heat and shivered in the winter’s cold while helping to build the U.S. Capitol.

Congress took note of their service and sacrifice Wednesday by erecting commemorative plaques inside the Capitol in their honor. Lawmakers said the memorials will ensure that the contributions of slaves in building one of the world’s most recognizable buildings will never again be forgotten.

“In remembering the slaves who labored here, we give them in death some measure of the dignity they were so cruelly denied in life,” Senate Republican leader Mitch McConnell said at the plaques’ unveiling.

The plaques read: “This original exterior wall was constructed between 1793 and 1800 of sandstone quarried by laborers, including enslaved African Americans who were an important part of the work force that built the United States Capitol.”

Lawmakers have been looking for ways to honor the slaves who were used in the construction of government buildings, including the Capitol and the White House.

Democratic Rep. John Lewis, a former civil rights leader from Georgia, who chaired a congressional task force that studied the contributions of slaves to the Capitol’s construction, told onlookers that the plaques help reveal a part of the Capitol’s history that has been overlooked by many.

“Imagine, in Washington’s oppressive summer heat and humidity, to chisel and pull massive stones out of a snake- and mosquito-infested quarry,” Lewis said. “Imagine, having to fight through the bone-chilling winter in rags and sometimes without shoes. Just imagine, the United States government paying your owner, not you, but your owner $5 a month for your labor. This Capitol, the most recognizable symbol of our democracy, was not built overnight, it was not built by machines. It was built through the backbreaking work of laborers and slave laborers.”

House Speaker Nancy Pelosi and Senate Majority Leader Harry Reid, both Democrats, along with their Republican counterparts McConnell and House Republican Leader John Boehner, unveiled the plaques inside the Capitol’s historic Mansfield Room. They will next be placed in the Congressional Visitor Center; its largest room is called “Emancipation Hall” in honor of the slaves’ work on the Capitol.

Historians have discovered that slaves worked 12-hour days, six days a week on construction of the Capitol. The federal government rented the slaves from local slave owners at a rate of $5 per worker per month.

Besides working on the building, slaves worked in quarries extracting the stone for the Capitol. Other slaves provided carpentry skills, and still others worked at sawing stone and timber.

Slave women and children were used to mold clay in kilns.

Lawmakers recounted for the standing-room only crowd the story of Philip Reid, perhaps the most famous of the slaves who worked on the construction of the Capitol. Reid was owned by a Maryland sculptor and ironworker who had been contracted to bronze a plaster copy of the Statue of Freedom, the statue that sits today on top of the Capitol Dome.

When the worker who had assembled the plaster model at the Capitol refused to disassemble it until he was paid extra money, Reid — a mulatto slave from South Carolina — was the only person who was able to figure out how to separate the sections so they could be moved to the foundry for casting.

Reid later is believed to be the person put in charge of bronzing the Statue of Freedom and was officially thanked for his work in an address to Congress in 1928 by one of the statue’s admirers.

The original plaster model of the Statue of Freedom that was worked on by Reid now sits in Emancipation Hall.

Reid also was one of the few slaves who was paid for his work at the Capitol, working for $1.25 a Sunday “keeping up fires under the moulds” — or keeping the ironworking fires hot so they would not have to wait on Mondays for new fires to be lit — according to a pay receipt. His receipt is signed with an “X,” suggesting that Reid was illiterate.

“We stand here today not only because of Philip Reid but for other enslaved African Americans like him who worked tirelessly and sacrificed,” said Democratic Sen. Blanche Lincoln, who also worked on the Congressional Slave Labor Task Force. “These plaques, in their own right, will serve as a symbol of their sacrifice and will be seen by visitors who enter the building forevermore.”

Copyright 2010 The Associated Press.