- The partially restored Fort Warren, an impressive granite Third System fortification designated as a National Historic Landmark, has stood on George's Island as a major defensive post for the protection of the harbor in every conflict from the Civil War through World War II.
- Fort Warren was built between 1834 and 1860 of massive blocks of Quincy granite.
- During the Civil War, Union soldiers were trained at Fort Warren and Confederate soldiers were imprisoned there.
- Fort Warren is said to be inhabited by "The Lady in Black," the ghost of a prisoner's wife.
- Historian Edward Rowe Snow has asserted that Fort Warren "has more memories of the Civil War days than any other place in New England."
- Another historian has claimed that soldiers working on the fort's parade ground invented the lyrics to "John Brown's Body." Set to the tune of a popular hymn, the song was so popular among Union troops that President Lincoln is alleged to have asked Julia Ward Howe to write a patriotic poem to the same melody, what became "The Battle Hymn of the Republic."
- Gallops Island quartered the Mass 54th Colored Regiment during the Civil War. Their story was later immortalized in the movie "Glory."