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