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"You shall have a place outside the camp and you shall go out to it; and you shall have a stick with your weapons; and when you sit down outside, you shall
dig a hole with it, and turn back and cover up your excrement."
Deuteronomy 23:12
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Origins
The Fifth Book of Moses - Deuteronomy, verse 23:12 could be regarded as the (or one of the) first municipal waste ordinances, ordering human waste be kept out
of residential areas.
For practical reasons, sewers were the convenient choice to transport waste out of the resident's way. The word itself - sewer - derives from the old French
"seuwiere" ("essevour"), meaning "to drain" or "to cause to flow".
Prior to sewage systems, many pre-18th century houses made use of cesspits underneath their homes - or simply let their waste flow directly on the street. Upon
reaching a certain level, the cesspits were designed to overflow; giving the streets the burden of transporting the waste to the closest body of water.
Waste Problems
The difficulties with the overflow method were plentiful. Aside from the nauseating stench emanating from (and in) the houses, not all waste was truly "fluid". The
cesspit overflow mechanism constantly clogged, causing structural damage and, more often than not, contamination of ground water sources (wells). "Mysterious" cases
of asphyxiation of entire families baffled officials, explosions in residential areas became commonplace - the result of hydrogen sulfide gases created by the
decomposing waste. Cholera, Plague and other diseases were easily transmitted, with thousands of cases in cities such as London, England alone.
Solution
Channels, or drainage conduits, were created underneath the streets in an effort to keep the waste away from the structures, and allow it to flow away from the
residential areas. An initial problem was that the conduits leading away from the structures and to the actual underground drainage channels weren't actually vertical.
They were slanted. And waste didn't flow easily to the channel, as there was no water pushing it forward. Maintenance workers were frequetly needed to shovel the
waste clear of the conduits and into the channels.
However - there was no easy street access to the conduits, meaning the workers would have to either dig their way down, or most likely, enter through the actual toilet
hole. The toilets themselves thus became manholes.
Extensive studies over many years were conducted to better determine the form and size of the conduits, and ensure that sanitation workers would
have easier access to the system for maintenance.
Street level channels would lead to the waste conduits, giving access to the sewers, while also acting as ventilation to prevent gas build-up. These channels - or
manholes - leading to the modern "Underworld" of society, needed obvious covers; easy for workers to access, yet hard for residents to accidentally fall in or steal. Round,
cast-iron manhole covers were an efficient choice over square for a few simple reasons.
One reason were the actual conduits - the holes that had been dug and that were fortified with brick (in Victorian times), were cylindrical - the strongest form for the underground
purpose (pressure equally distributed). The best fit for a cylinder is quite simply a round cover. Another reason was transportation and installation. Rolling covers could make life easier. Then - the shape could assist preventing the covers
from falling in the manholes once removed (although additional ledges under the covers keep them in place).
Manhole Cover Design
Manhole cover design varies greatly from city to city, with each municipality balancing budget versus art. Some cities, such as Seattle, opted for a clever street map
design on their covers, others went with city logos or seals. Most, though, choose a simple grid pattern, or checkered design. The reason behind a pattern or design
on the covers is simple - traction - both for pedestrians, as for vehicles.
As of late, manhole cover design is no longer something to be treaded on lightly. Cities like Vancouver, Seattle, New York and Tokyo have decided to pursue commissioned
designer covers, giving their cities more than just a curiousity. In competitions to find the best designs, these cities have their communities actively participating
in waste awareness, while simultaneously promoting a brighter and livelier city.
Manhole Covers in Antiquity
Aside from sewage systems, which only became common use in the past few centuries, manhole covers were in use thousands of years ago to cover access ports to water supply
conduits. Either large slabs of wood or stone, documented use can be found i.e. by the Romans for the Aqueducts. The basic design of the slabs may have varied in size, but
remained the same from Roman times up until approx. the 18-19th century.
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