Flentje, Ernst, House
Why it's listed
Built in 1866 at 129 Magazine Street in Cambridgeport, this wooden house began as a Mansard-style single-family residence for Sylvester H. Sanborn, a book bindery owner who later served as a city alderman and common councilman. It was one of six mansions erected for prosperous local businessmen when upper Magazine Street was a fashionable district. In 1900 owner Ernst Flentje had it converted into a three-story apartment building, designed by architect William Clark in an elaborate Colonial Revival style. Twin curved, three-tier porches form a heart-shaped plan with swell-front bays. A Cambridge survey director called it the most exaggeratedly elaborate three-decker in Cambridgeport. The conversion reflects shifting social conditions: the first generation of mansion owners was dying off, and electrified street cars after 1895 drew a new middle class to the area. The house illustrates how the three-decker gained acceptance through decorative detail, and it was listed for its association with that trend and for its architecture.
Significance in brief: The nomination argues the house is the stylistic epitome of the three-decker type in Cambridge, described by a survey director as the most exaggeratedly elaborate in Cambridgeport. Its conversion from a mansion to an opulent three-decker reflects social change in Cambridgeport around 1900, when the three-decker gained acceptance as middle-class housing through architectural elaboration.
Machine-generated summary. This summary was generated by a language model from the official nomination document and has not been reviewed line by line by an editor. It may contain errors. Check the source document before relying on any detail. Source: nomination document (PDF) · National Archives catalog entry. NRHP reference 83000800, listed June 30, 1983. Summary generated October 2026 (model claude-sonnet-5-5, prompt v1.0-2026-10-29, confidence medium).
Key facts
| Address | 129 Magazine St., Cambridge |
|---|---|
| County | Middlesex County |
| Listed | June 30, 1983 |
| Reference number | 83000800 |
| Resource type | Building |
| Architect / builder | William Clark, architect (1900 remodelling); Ernst Flentje, owner who converted it |
| Architectural style | Colonial Revival (remodelled 1900 from a Mansard-style house) |
| Criteria |
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| Areas of significance | Architecture |
| Level of significance | Local |
| Status (as stated in the nomination) | Present use is residential. |
| Acreage | 0.9 |
| Coordinates | 42.35907, -71.11134 (NPS GIS) |
What listing means for this property
National Register listing is honorary for a privately owned home: it does not by itself restrict what an owner may do with their own money, and it does not require public access. Restrictions come from local landmark or historic-district ordinances, which are separate (how they differ).
Owner-occupied houses are not eligible for the 20% federal rehabilitation tax credit, which applies to income-producing buildings, but many states offer credits for homeowners. Listing also opens the door to preservation easements and to buying a plaque. Start with what listing means for homeowners, renovating a listed house and selling one.
General information, not legal or tax advice. Rules change; confirm with your State Historic Preservation Office or a qualified adviser.
Sources and further reading
- National Park Service, National Register of Historic Places database (snapshot May 2026), reference 83000800.
- Nomination form (PDF, National Archives) — catalog entry
- Wikipedia article (used for cross-checking only; text not reproduced here)
- Wikidata Q5394983
- This listing as JSON
Last updated October 2026. Found an error? See the editorial policy for how to report it.