With an audience of about 500 donors, potential donors, and members of the university community, University of Pennsylvania officials  Wednesday formally announced the kickoff of a massive renovation project for the Penn Museum of Archaeology and Anthropology, the most extensive makeover in the storied building's 118-year history.

Penn president Amy Gutmann vowed that at the conclusion of the multiyear project, the museum's collection of 12,000 skeletons would no longer be figuratively in the closet.

"These skeletons in our closet are not to be hidden," she announced. They are, in fact, "tools of discovery."

"This is the museum's moment," she said.

The project will proceed in three phases. The first, which should be complete by summer  2019, entails renovation of the Middle Eastern, Mexico and Central America, and Africa galleries, allowing for many more artifacts to be displayed.

The second phase, beginning at some point later in 2019, will, most dramatically, include extensive work on the museum's 15,000-square-foot Egyptian galleries. Once that work is complete, the museum will be able to display architectural fragments from a royal palace that have never been shown in their entirety because of their weight. Shored-up flooring will make this possible for the first time.

The third phase will renovate the museum rotunda and its Asian galleries.

In addition to the initial gallery renovations, the first phase will open up the main entrance off South Street and add a gallery to greet visitors. Air-conditioning will be installed in the Harrison Auditorium and surrounding galleries. About 44,000 square feet of galleries and public spaces will be renovated and retooled.

Richard Gluckman of New York's Gluckman Tang Architects, designers of the overall project, promised work would be historically sensitive to the building and would let in the light. The Gluckman Tang design also promises a rationalization of the museum's interior that will make the whole easier for visitors to navigate.

Penn officials have said the first phase of the project will cost $21 million. They declined to say what the overall costs will be.

Julian Siggers, museum director, promised  the result will be dazzling.