How Long Sewer Tunnels Can Last

A recent article on he telegraph.co.uk website drew my attention to the current plight of the currently-functioning, ancient Roman sewer system which is undergoing renovation to prevent its collapse.  Of course, there's been some work on it over the years but it amazes me that a mile long tunnel can be maintained for over 2,000 years (it began as a canal around 500 BC, in the time of King Tarquin) with relatively little change to its original engineering.  Read more here!