The Joseph Sinnott Mansion, also known in Gaelic as "Rathalla," meaning "home of the chieftain on the highest hill" is the Main Building at Rosemont College.

[2] Edward Hazelhurst and Samuel Huckel were both fellows of the American Institute of Architects [3] Rathalla is a 2+1⁄2-story, thirty-two-room, 27,712 sq ft (2,574.5 m2) stone building that sits on a brick foundation and was designed in a Renaissance Revival/Châteauesque style.

[4] This mansion features a high, steep-sided, slate covered hipped roof, six decorated chimneys, numerous dormer windows, turrets, and stone carvings including gargoyles.

The stained glass window above the staircase features the Sinnott family's coat of arms, containing the motto "Ama Deum et Serva Mandata."

New wiring, heating and air conditioning, modern plumbing, an elevator, chair lift, and a handicapped accessible bedroom were all added.