The Embanking of the tidal Thames is the historical process by which the lower River Thames, at one time a broad, shallow waterway winding through malarious marshlands, has been transformed by human intervention into a deep, narrow tidal canal flowing between solid artificial walls, and restrained by these at high tide. The Victorian civil engineering works in central London, usually called "the Embankment", are just a small part of the process.
With small beginnings in Roman Londinium, it was pursued more vigorously in the Middle Ages. Mostly it was achieved by farmers reclaiming marshland and building protective embankments or, in London, frontagers pushing out into the stream to get more riverfront property. Today, over 200 miles of walls line the river's banks from Teddington down to its mouth in the North Sea; they defend a tidal flood plain where 1.25 million people work and live.
Since the Thames has a large tidal amplitude, early modern thinkers could not believe local people were capable of building mighty embankments beside it; hence the works were attributed to "the Romans". The current explanation is that tides were small at first, requiring modest embankments only; as the sea has gradually invaded the Thames valley, the embankments have been raised to match in easy stages.
It has been argued that land reclamation in the Thames contributed to the decay of the feudal system. Other political consequences were said to be two clauses in Magna Carta, and one of the declared causes of the English Civil War. The deepening of the Thames made it navigable by larger ships that could travel further inland: an unforeseen result was the growth of the world's largest port. Much of present-day London is recovered marshland, and considerable parts lie below high water mark. Some London streets originated as tracks running along the wall and yet today, are not even in sight of the river.