Until the late 16th century most of what we now know as London was still covered in the famous Winchel Sea. When the land was reclaimed and that sea forced underground by Yentob The Engineer a ring of dykes was established around the city - in case serious flooding ever returned. This set, near SOAS, is one of the few remaining above ground and is a favourite for Yentob completists on tour. Why they survive, however, is less well known. This is because, in the 1970s, the Office of the Air Marshall - looking to extend the High Speed Cycle routes from Regents Park down to Russell Square Agricultural College - decided to try and artificially alter the thick air currents through the use of specially developed ‘Air Mills’. They had the Back Dykes clad in concrete and used them as mounting points for their experimental systems - removed again in the 1980s.