The Back Bay was designed to include a series of alleys that run behind the houses.  These alleys originally were intended for deliveries, which could be received directly into the kitchen areas, which usually were located on the ground level in the back of the houses.

In his Houses of Boston’s Back Bay, Bainbridge Bunting notes that “The obvious advantage of the alley is that it leaves the front of the house completely free of kitchen entrance and service areas.  In New York, where there are no alleys, the necessary service elements could never be entirely hidden under the high stoop, and in the Back Bay, where there was no long flight of steps leading to the front entrance, the designer would have had even more serious trouble disguising service facilities at the front of the house.  The presence of a service alley in the Back Bay, therefore, was a desirable feature, and it kept delivery wagons off the main streets.”

Today, the alleys serve as access to parking areas behind the houses and, on occasion, to the primary entrance of apartments or condominiums in subdivided buildings.

The alleys are 16 feet wide, including sidewalks on both sides (frequently occupied by dumpsters or by automobiles parked illegally so that they extend to the curb).

Originally, all of the alleys were private, with each property owner owning the land to the middle of the passageway and each deed containing easements for common passage and drainage by the owners of the other lots on the block. As private property, the alleys were the responsibility of the owners, not the city, to maintain. Inattention and inability to reach agreement among the owners about maintenance led to significant deterioration.

In the 1890s, the poor maintenance and condition of the alleys became a matter of increasing public concern. On November 8, 1897, the Boston Evening Transcript published an editorial calling attention to Our Troublesome Alleys,” commenting that “there is likely to be an offensive and disease-breeding condition before anyone is aware of it, or at least before anyone has taken steps to correct it.”

In 1898, the Massachusetts Legislature granted the City of Boston the authority to take jurisdiction over alleys 25 feet or less in width (Chapter 298, Acts of 1898). The City subsequently designated all but three alleys in the residential portion of the Back Bay as public alleys and took responsibility for their maintenance. The exceptions were Alleys 917, 918, and 919, the connecting alleys between Commonwealth and Newbury in the block between Massachusetts Avenue and Charlesgate East, which remained private ways as of 2021. The City also did not take jurisdiction over Back Street, which is thirty feet wide and therefore was excluded from the 1898 legislation; it also remained a private way as of 2021.

Between Arlington and Massachusetts Avenue, the alleys run east-west and each block has a different Public Alley number.  The alley numbers between Beacon and Marlborough increase each block to the east from Massachusetts Avenue to Arlington (Alley 414 to Alley 421). The alley numbers between Marlborough and Commonwealth decrease each block to the east from Massachusetts Avenue to Arlington (Alley 422 to Alley 429). And the alley numbers between Commonwealth and Newbury increase to the east each block from Massachusetts Avenue to Arlington (Alley 430 to Alley 437).

The alleys system continues west of Massachusetts Avenue, but in a modified arrangement.

Alley 908 runs west from Massachusetts Avenue between Beacon and Marlborough, but ends at the eastern property line of the Barnes Mansion condominium at 10 Charlesgate East.  At that point, it turns south and continues to Marlborough.

Alley 905 runs west from Massachusetts Avenue between Marlborough and Commonwealth to the rear of 428 Marlborough and of 379 Commonwealth. At that point, it turns north, narrows to fourteen feet in width, and runs to Marlborough (between 428 and 430 Marlborough). A five foot wide branch continues west behind 430-440 Marlborough to the north and 379-389 Commonwealth to the south, where it stops.  Each Commonwealth Avenue lot further west, starting with 393 Commonwealth, extends north to Marlborough, with no alley.

Alley 918 does not connect with Massachusetts Avenue, but rather runs between Commonwealth and Newbury starting at the east behind 378 Commonwealth and ending at the west at The Somerset at 400 Commonwealth.  On the east, from behind 378 Commonwealth, Alley 917 runs from Alley 918 to Newbury; to the west, Alley 919 runs behind the eastern side of The Somerset to Newbury.

Alleys between Beacon and Marlborough

421     Between Arlington and Berkeley

420     Between Berkeley and Clarendon

419     Between Clarendon and Dartmouth

418     Between Dartmouth and Exeter

417     Between Exeter and Fairfield

416     Between Fairfield and Gloucester

415     Between Gloucester and Hereford

414     Between Hereford and Massachusetts

908     From Massachusetts west to 10 Charlesgate East, and then south to Marlborough

Alleys between Marlborough and Commonwealth

422     Between Arlington and Berkeley

423     Between Berkeley and Clarendon

424     Between Clarendon and Dartmouth

425     Between Dartmouth and Exeter

426     Between Exeter and Fairfield

427     Between Fairfield and Gloucester

428     Between Gloucester and Hereford

429     Between Hereford and Massachusetts

905     From Massachusetts west to 428 Marlborough and then north to Marlborough

Alleys between Commonwealth and Newbury

437     Between Arlington and Berkeley

436     Between Berkeley and Clarendon

435     Between Clarendon and Dartmouth

434     Between Dartmouth and Exeter

433     Between Exeter and Fairfield

432     Between Fairfield and Gloucester

431     Between Gloucester and Hereford

430     Between Hereford and Massachusetts

917     Between Newbury and Alley 918, at 378 Commonwealth

918     Between Alley 917 and Alley 919, from 378 Commonwealth to 400 Commonwealth

919     Between Newbury and Alley 918, at 400 Commonwealth