The Merrimack-Middle Streets Historic District is significant as the heart of Lowell’s central business district. Buildings found in the district date primarily from the 1830s to the early 1900s and include examples of many architectural styles including Federal, Greek Revival, Italianate, Second Empire, Queen Anne, Romanesque, and Renaissance Revival as well as an early, prototypical skyscraper.  Listed on the National Register of Historic Places in 1979 with a boundary increase in 1988, the district includes 67 structures.