WASHINGTON — President Barack Obama today took a shuttered Army fort in Virginia with an important role in the nation’s slavery history and made it a national monument.

Using his authority under a century-old law, Obama signed a proclamation designating Fort Monroe a national monument. That saves it from major development and preserves its history for generations.

At a signing ceremony in the Oval Office, Obama said the fort had played a “remarkable role in the history of our nation.” He said he looked forward to visiting and taking daughters Malia and Sasha along to “get a sense of their history.”

The fort and the land it sits on are historically significant because it was where Dutch traders first brought enslaved Africans in 1619. It remained in Union possession during the Civil War and became a place where escaped slaves could find refuge. Confederate President Jefferson Davis also was imprisoned there after the Civil War.

Obama said the fort also helped create the environment that led President Abraham Lincoln to sign the Emancipation Proclamation.

But the government decided in a 2005 cost-cutting move to close the fort and many other military installations. In September, the Army ended its 188-year presence there.