More than 1,800 knitters have covered the Andy Warhol Bridge in the U.S. with colorful yarn.

Volunteers worked all weekend to attach 580 blanket-size, hand-knitted panels to the pedestrian walkways on the bridge in Pittsburgh, the city where Warhol was born.

The project was organized by the Fiberarts Guild of Pittsburgh and other local institutions.

The guild calls it the nation's largest "yarn bomb." The term applies to artists who knit coverings for everyday objects like lampposts, street signs and trees.

The bridge will be covered in the yarn _ 3,000 feet (914 meters) of it _ until Sept. 6.

The planning started about 18 months ago, said Amanda Gross, 29, who had the idea for the project.

She said yarn bombing is "really inspirational" and a good way to bring communities together.

The group ultimately had to work with designers, lawyers, architects, structural engineers and riggers to make the idea a reality.

Sherri Roberts, 60, a past president of the guild, said the group decided that the panels would contain only colors and designs _ no words or political or religious symbols.