I can find very little information about the history of this property. The Great Parade Fire of 1802 burned every building on Market Street. In 1803, Portsmouth widened the street and built many of the brick buildings that still remain near Market Square. Although the Great Market Street Fire of 1845 destroyed several brick blocks, I believe the flames traveled only as far as Ladd Street and Commercial Alley. For those reasons, I estimate the date of construction to have been 1803.
The photograph below appeared in my favorite source for vintage photographs of the city, C. S. Gurney's 1902 book, Portsmouth . . . Historic and Picturesque. Like the Portsmouth Brewery building and several other merchants on Market Street, a dry goods store sold their wares here at the turn of the 19th Century. This one belonged to D. F. "Fred" Borthwick, who was also a trustee of the Portsmouth Savings Bank.
The Portsmouth Directory of 1905 lists the address of D. F. Borthwick's as 11 and 13 Market Street; however, the street has been renumbered. To find the building, I printed the old photograph and carried it with me on a search down Market Street. The 2nd and 3rd floors are almost identical in both pictures and helped me to identify the building.
The store front has changed considerably! Later owners removed the door on the right to expand the retail space, installed a new entrance on the left, relocated the hexagonal sales pavilion to accomodate the new configuration, and lowered the awning. The left door in the vintage photo now opens on two clothing stores: Angelica's Muse on the left and Clay's on the right. The new entrance opens on LeRoux Kitchen, which occupies the building next door.