See also: https://en.wikipedia.org/wiki/Xerxes_Canal

"a navigable canal through the base of the Mount Athos peninsula in Chalkidiki, northern Greece, built by king Xerxes I of Persia in the 5th century BCE. [...] The total length of the canal was two km, its width was 30 meters, and it was three meters deep, enough for a trireme to pass."