Turn-of-the-century luxury

The ballroom at 5 Commonwealth Avenue is a jewelbox.

That's what William Young, the city's architectural guru at the Back Bay Historical Commission, calls it.

It's an odd term for a ballroom that is bigger than many city condominiums. But he's right. The curved soffits, the gilt-trimmed walls, columns and ceiling -- in the style of French King Louix XVI --are a tight, seamless box that seems almost cozy, despite its size.

The Mercury statue standing sentinel in the library, the fountain featuring a little boy in a wing off the ballroom, the scene of boys playing on a marble frieze in one bedroom -- all are sumptuous carvings in white marble that are rare even in Back Bay's exquisitely appointed interiors.

That's because Walter C. Baylies, a flourishing cotton broker whose family hailed from New York, decided to knock down the brownstone on that lot and build his own, elaborately ornate house in the early 20th century.