A simple link to complex systems
Rabbits, woodchucks, and other burrowing creatures are moving into the sunlight to reconnoiter lawns and gardens. Homeowners worry about moles and grubs, and marvel at the tiny openings made by birds hunting larvae lurking below the grass. Any small hole might shelter a snake or conceal a chipmunk, and in spring such holes appear everywhere.
Potholes appear everywhere too, angering motorists and testing the patience of highway departments. Potholes are unplanned cavities, and even worse, uncovered ones.
The word manhole is originally as nautical as porthole. Into the middle 19th century it designated a hatch barely large enough to accommodate a seaman. While larger hatches opened to load cargo, the manhole might be opened only to inspect a hold or for emergency escape. The oval opening in a fiberglass kayak is still formally called a manhole.
Nautical terminology also perhaps gave English the word sewer, which may be a corruption of the term seaward, although experts think sewer evolved from an Old French term still echoing in the modern word sluice. Until about 1800, drains, gutters, sluices, and sewers ran open to the sky, and tended downhill, in coastal cities toward the sea. By about 1850 sewers ran under cover, as some had as early as 3500 BC in southern Europe. In most cities, rain flowed from roofs into gutters, down downspouts and conductor pipes, then into street gutters or storm drains, where it merged with the sewage that usually flowed in pipes. Covered sewers reduced odors and other unpleasantness, but 18th-century city people knew them as finicky. While downpours might flush them clean, often they jammed and overflowed.
In ancient times only a few Mediterranean cities enjoyed covered sewers. Since the first paved sewers were essentially stone-covered ditches -- sometimes lined with stone or brick -- that twisted down the middle of narrow paved city streets, crawling through them proved impossible. Instead, every few yards builders placed large slabs of wood or stone as access panels. When sewage backed up, workers pried up the first stone downstream of the blockage and probed with long poles to dislodge the obstruction.
By the 1830s, most United States cities had embarked on massive water-supply and sewer-building projects, chiefly to prevent yellow fever and other virulent diseases transmitted through polluted drinking water. In the 1860s, sanitary engineers had started designing sewers oval in cross section, with the narrow ends of the oval pointed down and up to avoid blockages. But any lining irregularity seemed to produce a jam over time, and by 1900 experts had abandoned brick-by-brick construction for large-diameter, smooth-lined clay pipe. But jams still occasionally blocked pipes, and experts insisted on access points.
Laying sewer mains far below ground to forestall freezing meant designing vertical shafts, often fitted with iron rungs as ladders. Five to 10 feet below the pavement, the shafts intersected the gently sloping sewers. At pavement level, the shafts met a cast-iron ring whose inner ledge supported a circular cast-iron disk, some of which weighed up to 300 pounds. The disks easily carried the weight of horses and wagons, and their patterned surfaces kept horses and pedestrians from slipping in rain. More importantly, the covers never moved under weight so long as workers swept clean the casing.
Manhole covers conceal the access shafts to sewers and to storm-drain systems, too. Astute walkers can trace the intersections of storm-drain systems, which by law are separate from sewage systems. In Quincy, Brockton, and other older, sophisticated cities, manholes offer access to subterranean electric, telephone, and other utility lines.
And in the end, the word manhole escaped the 1970s gender-free speech reform movement. No one speaks of ''person holes" today, but then again, few people mention manholes either -- until trouble pops up like some rabid rodent.
Norwell resident John Stilgoe is Orchard Professor in the History of Landscape at Harvard University.
