Slight tangent: The world's first tunnel under a river was completed by Brunel in 1843 and is still in use today by Transport for London for as part of the Lon

Slight tangent: The world's first tunnel under a river was completed by Brunel in 1843 and is still in use today by Transport for London for as part of the London Overground network (ignore the confusing naming - the Overground is like the Underground, but the service operates at longer intervals). The Wikipedia page has a lot of detail about how it was constructed: https://en.wikipedia.org/wiki/Thames_Tunnel https://en.wikipedia.org/wiki/Thames_Tunnel