The Byron Greenough Block or Lower H. H. Hay Block is an historic block in downtown Portland Maine. Located at the intersection of Free Street and Middle Street in Portland's Old Port. It was built in 1848 by Byron Greenough who made his wealth in hatting and clothier. The architecture firm Stevens and Stevens designed and added the fourth floor. The block was listed on the National Register of Historic Places in March 1977. Given a list of categories: company, educational institution, artist, athlete, office holder, mean of transportation, building, natural place, village, animal, plant, album, film or written work, what category does the paragraph belong to?
The answer to this question is:
Building