Dauphin County Bridge No. 27
Also known as: Seaman Bridge
Why it's listed
Built in 1896 by the Chambersburg Bridge Company, this metal truss bridge crosses Mahantango Creek between Mifflin Township in Dauphin County and Lower Mahanoy Township in Northumberland County. It measures 162.5 feet long, with ten 16-foot-3-inch panels, and rests on stone abutments. Its design is a variant of the Baltimore truss. Its upper built-up verticals are used in compression and its lower verticals in tension, the reverse of the usual Baltimore arrangement, and the document treats this as the reason for its significance. The bridge survived the 1972 flood undamaged. It was closed to vehicles in 1983 and to pedestrians in March 1992. Nearby residents of a cul-de-sac relied on it for emergency egress, and its closure forces a 2.5-mile detour. The document describes its historic integrity as excellent and recommends rehabilitation.
Significance in brief: The bridge is presented as an excellent example of a late nineteenth century metal truss bridge, notable for its 162.5-foot span. Its truss design is described as a variation of the Baltimore truss, with the vertical members loaded in reverse of the usual arrangement. It is also argued to be important to nearby residents, who would face long detours if it were unavailable for access.
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 93000720, listed August 2, 1993. Summary generated October 2026 (model claude-haiku-5-5, prompt v1.1-2026-10-29, confidence medium).
Key facts
| Address | Deibler's Dam Rd. (Mahantango Creek Rd.) across Mahantango Cr. (Mifflin and Lower Mahanoy Townships), Pillow |
|---|---|
| County | Dauphin County |
| Listed | August 2, 1993 |
| Reference number | 93000720 |
| Resource type | Structure |
| Period of significance | 1896 |
| Architect / builder | Chambersburg Bridge Company (builder) |
| Architectural style | Metal truss bridge; variant of the Baltimore truss type |
| Criteria |
|
| Areas of significance | Engineering |
| Level of significance | Local |
| Status (as stated in the nomination) | Closed to vehicular traffic since 1983 and restricted to both vehicles and pedestrians; pedestrian crossing ended March 1992. |
| Acreage | 0.9 |
| Coordinates | 40.63486, -76.85606 (NPS GIS) |
What listing means for this property
For a publicly owned building or structure, listing mainly matters when federal funds, permits or licences are involved: projects then go through Section 106 review so effects on the property are considered. Listing also strengthens applications for preservation grants and, for leased income-producing uses, can enable the federal rehabilitation tax credit.
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 93000720.
- Nomination form (PDF, National Archives) — catalog entry
- Wikipedia article (used for cross-checking only; text not reproduced here)
- Wikidata Q5228066
- This listing as JSON
Last updated October 2026. Found an error? See the editorial policy for how to report it.