WASHINGTON (AP) — The Smithsonian's National Postal Museum has begun construction to expand the Capitol Hill museum with a new gallery showcasing a collection of more than 20,000 objects.

The museum is expanding in its current location next to Washington's Union Station. It is taking over the former Capital City Brewery restaurant space to create a new 12,000-square-foot gallery.

The William H. Gross Stamp Gallery will be named for its primary benefactor. Gross, founder of Pacific Investment Management Co., donated $8 million to fund the expansion.

The museum says the new gallery will include thousands of stamps, a wall of windows featuring stamp art, a welcome center in the building's historic postal lobby, a postmaster's suite featuring special exhibits and new education spaces.

The new gallery is scheduled to open in September 2013.