Astrologers predicted that on this day in 1524, because of a Grand Conjunction of all seven major planets, “the waters of the Thames would swell to such a height as to overflow the whole city of London, and wash away ten thousand houses” (among other things). Heeding the warning, broadcast far and wide in print, many thousands of the city’s inhabitants withdrew to high dry ground, as at Hampstead and Highgate to the north and Blackheath to the south (it is said that William Bolton, the Prior of St Bartholomew’s, took refuge in a specially constructed and provisioned tower at his residence in Harrow). Needless to say, in the event, the predicted tidal wave never materialised.
On a more-or-less related note, on this day in 1953, there was a terrible flood in the Thames Estuary that drowned hundreds of people. Also, on this day in 1983, the Thames Barrier was raised for the first time.