MAINE’S COVERED BRIDGES, by Joseph D. Conwill, Images of America series, Arcadia Publishing, Dover, N.H., 2003, 128 pages, $19.99.

Do you know why bridges were covered?

Was it to comfort horses, which calmly entered the barnlike spans while trotting across a river? Or because Yankees liked building big, wooden, roofed structures? Or was it to protect the bridges’ intricate underpinning?

If you selected the third answer, you win, if not a covered bridge, then a chance to read Joseph Conwill’s sparkling photographic history of Maine’s covered treasures, the most thorough book to date on the topic. Sadly, most of the book’s more than 200 photographs show bridges from yesteryear, since a state that once boasted 150 such spans now has only nine, two of which are modern replicas; fire, flooding and road rebuilding claimed the rest.

The bridges “were covered simply to protect the timber trusswork from decay,” writes the Rangeley photographer, historian and editor of the publication Covered Bridge Topics. Because the bridges’ main components are wooden, he states, they will decay unless protected from the weather.

Like Arcadia Publishing’s numerous other titles, the meat is in the crisp, clear black-and-white pictures. Conwill’s images, culled from Maine Department of Transportation files and other public and private sources, evoke the 19th century ingenuity that erected the sturdy bridges, of dizzying lengths and designs, over Maine’s major rivers – the Penobscot, Androscoggin, Saco, Kennebec and Aroostook – and such minor ones as the Narraguagus and Piscataquis.

Five covered bridges once spanned the Kenduskeag Stream; three in Bangor, one in Glenburn, and the fifth, the shingled Robyville Bridge, in Corinth. The latter, pictured on the book’s front cover, is the sole survivor of the five.

Several photos show bridges that my family and I visited in the 1960s, when I was a teenage, camera-clicking history buff. Eventually I photographed them all, from Littleton, in Aroostook County, to Wilsons Mills, in Oxford County. The rest are located in Newry, Porter-Parsonsfield, Gorham-Windham (replaced following a 1973 fire), Andover, Fryeburg, Corinth and Guilford-Sangerville (replaced after a 1987 flood).

Conwill’s photo captions are informative, and because he has visited every covered bridge in North America, he knows his stuff. At times, though, they lack a colorful human touch, though to be fair, the book’s space constraints don’t allow for much elaboration. Covered bridges are more than wood and shingle nails, after all. They’re about rope swings and swimming holes, and, as fans of “The Bridges of Madison County” can attest, they’re also brimming with romance (our ancestors didn’t call them “kissing bridges” for nothing).

The author does mention the day that Jumbo, the circus elephant, lumbered through the Ferry Point Bridge that connected Calais with St. Stephen, New Brunswick. He also recalls the April 1, 1987, flood that swept away Low’s Bridge, over the Piscataquis River between Guilford and Sangerville. But what of the human drama that infused those events?

Bangor’s Morse Bridge, rebuilt after removal from a nearby location over the Kenduskeag Stream and burned by an arsonist in 1978, is pictured. The city had a covered railroad bridge, complete with draw span to allow schooners to sail up the stream as far as State Street Bridge; and a shared bridge with Brewer, a 792-foot-long span that replaced an earlier one built in 1831-32. Both were destroyed by flooding. The Maxfield Bridge, on Valley Avenue, was burned in 1944.

Maine’s first known covered bridge, in Augusta, was built in 1818 and burned down in 1827, replaced the same year by another bridge that stood until 1890. Some remarkable photos show bridges in Hampden (America’s only known covered bridge built for trolley car traffic), Eastport, Allagash, Milo, Dover-Foxcroft and Passadumkeag.

Preservationists mourned the loss of the double-lane Stillwater Bridge, at Old Town, removed in 1951. A favorite of photographers and artists, largely because of its unusual latticework design, the landmark was replaced by a nondescript highway bridge.

Conwill’s book is a fitting companion to last year’s “New Hampshire Covered Bridges,” by Glenn A. Knoblock, also published in the Images of America series. Another title on the covered bridges of New York state is due out next year.

Dick Shaw, a lifelong covered bridge enthusiast, has compiled five Maine books in the Images of America series. He can be reached at 990-8204 or rshaw@bangordailynews.net.