Hierarchy classification:

1. top of the aat hierarchies
2. Objects Facet
3. Built Environment (hierarchy name)
4. Single Built Works (hierarchy name)
5. single built works (built environment)
6. [single built works by specific type]
7. [single built works by function]
8. transportation structures
9. [transportation structures by form]
10. bridges (built works)
11. [bridges by form]

Anotations

Scope note:

Timber-truss structures carrying a roadway or railroad track over a river or other obstacle, characterized by the roof and siding forming an almost complete enclosure to protect the wooden structural members from the weather. There is no evidence of timber-truss bridges, with or without covering, in the ancient world; however, drawings survive of covered bridges dating from the 14th century and later in Europe. In North America covered timber bridges were common in the 18th through early 20th centuries, although they were gradually being replaced by metal truss bridges, which required no covering.