Some of the country's top research institutions have combined to launch a massive online archive.

The Digital Public Library of America began beta testing last week, promising a site with millions of materials ranging from images of George Washington to footage of Freedom Riders during the civil rights era. Directors of the digital library, first conceived in 2010, include officials from Harvard University and the University of Michigan and a former executive at Google Inc. Government support includes the National Endowment for the Humanities and the Institute of Museum and Library Services.

"Starting with over 2 million items, each with its own special story and significance, the Digital Public Library of America will now begin to assemble the riches of our country's libraries, archives and museums, and connect them with the public," executive director Dan Cohen wrote on the library's website.

The library had planned events at the Boston Public Library on April 18 to mark the opening, but it postponed them until the fall because of the bombings at the Boston Marathon. By the fall, the library also hopes to have launched the site in full.

Efforts by Google to build an online archive have run into legal problems over the Internet search engine's proposed use of copyrighted materials. Cohen said most, but not all, of the archives in the digital library are older works in the public domain. He said he would like to have discussions with book publishers about using more recent releases, perhaps including them several years after they first come out, "once the commercial window of sales has finished."