Battle flag carried by black Union troops hits auction block

A hand-painted flag carried into battle by a black Union regiment during the Civil War is going up for auction in Pennsylvania.

Morphy Auctions will sell off the piece of history June 13. Pre-bidding is underway online .

It's one of 11 such flags painted by African American artist David Bustill Bowser, the son of a fugitive slave. It's the only known surviving flag.

The auction house says seven others are known only from photographs. They were sent to the military museum at West Point in 1906, but were thrown out in the 1940s.

The flag up for auction depicts a black soldier waving goodbye to Columbia, the female personification of America, beneath a banner reading, "We Will Prove Ourselves Men."

The 127th Regimental banner is expected to fetch about $250,000.