A national historic landmark.
A large annex of yellow brick was built between 1896 and 198 by Charles E. Brigham.
Additional wings were built by Chapman, Sturgis & Andrews in 1914-1917
The dome, originally built with wood shingles, was covered with copper in 1802 by Paul Revere and Sons.
The dome was gilded in 1862.
The design was inspired by the 1778 Somerset House in London by Sir William Chambers.