Pontycysyllte Aqueduct...

... took 10 years to build and it finally opened in 1805 at a cost of £47,018.
It is the longest and highest aqueduct in Britain, and carries the canal 126ft above River Dee - and we tootled across it this morning on our way to Llangollen :)
Amazing construction ( rather than invention - sorry) from the 1800s - great theme Laurie!