an artificial canal in Greece that connects the Gulf of Corinth in the Ionian Sea with the Saronic Gulf in the Aegean Sea
It is 6.4 kilometres (4 miles) in length and only 24.6 metres (80.7 feet) wide at sea level, making it impassable for many modern ships
The Corinth canal concept originated with Periander of Corinth in the 7th century BC. Daunted by its enormity, he chose to implement the Diolkos, a land trackway for transporting ships, instead
Construction of a canal finally began under Roman Emperor Nero in 67 AD
Read more here https://en.wikipedia.org/wiki/Corinth_Canal
I find it incredible that there's differing tidal forces on either side of the canal, it makes sense since there are no locks, but that isn't something a lot of canals have to deal with.
Also water running past limestone is a problem under normal circumstances, water running past limestone at that sharp of an angle, you wouldn't catch me going through there (though now it's been reinforced).
The talk of the overland system that they used before the canal is kinda funny, 'it would take a hundred people to pull the vessel', I know exactly where they got those people (hint it was the sailors).