The first act providing for a commission of sewers in London dates from 1531.
These and other tributary streams have been covered in and built over (in some cases serving as sewers), but it is possible to trace their valleys at various points by the fall and rise of streets crossing them, and their names survive, as will be seen, in various modern applications.
The length of sewers in the main system is about 288 m., and their construction has cost about eight millions.
An appointive board of public service consists of a president and four directors of divisions, public welfare, public safety, public utilities, and streets and sewers.
Without resorting to this exaggeration, Mommsen can speak with perfect truth of the " enormous space occupied by the burial vaults of Christian Rome, not surpassed even by the cloacae or sewers of Republican Rome," but the data are too vague to warrant any attempt to define their dimensions.