Right here in downtown Portland, Maine, the Thompson Block occupies 117–125 Middle Street. Designed by George M. Harding and constructed in 1867, this 3½-story brick commercial block reads like a carefully composed piece of the Old Port. Its polychrome slate mansard roof gives it a full fourth floor, and the building's roughly trapezoidal shape sits where Middle Street met the head of the now-demolished Deer Street.
On the ground floor an arcade of iron supports forms arches over display windows and recessed store entries; above, a stone entablature separates the ground floor from the next two floors. Those upper floors are divided into six bays, articulated in a 1-1-2-1-1 pattern. To your left across Church Street is the Rackleff Building, another George M. Harding design; the less ornate brick commercial building across the narrow alley stands to the right.
Along with its neighbors, the Rackleff and Woodman Buildings, the Thompson Block creates one of the best-preserved period commercial street views in the entire state. It was added to the National Register of Historic Places on February 28, 1973. Follow the lines of the facade up to the mansard, then down Middle Street to those neighboring facades.