Did the Thames used to freeze over?
It's hard to imagine London's mighty river coming to a frozen standstill
Yes. Indeed, the Thames froze at London at least 23 times between 1408 and 1814, though several of these events lasted only a few days.
The freezing of the river in London, where ice is now rarely seen, was caused by three factors. First, the climate in Britain was on average about 1°C colder between about 1400 and 1800 than before or since. Second, the Thames was then wider and shallower than it is today, as it is now restricted between solid embankments. Finally, the numerous narrow arches of the medieval London Bridge partially blocked the water on the upstream side, reducing the flow.
During the big chill of 1683-4, the Thames froze for two months, with ice some 28cm thick, which provided a stage for the most famous of the London Frost Fairs.