40 times since 1142 the Thames river in has frozen solid. Starting with the freeze in 1608 Londoners began throwing an impromptu fair on the river – The Frost Fair.
The river was much wider and slower before the modern embankments, and the old London Bridge acted as a partial dam because the piers were large and set close together restricting the flow of water. These days the river is deeper and flows faster than it did in past centuries.
The last frost fair was in 1814, it began on 1 February, and lasted four days. It must have been amazing to see the river solid; to have what was a barrier suddenly become easily transverse-able. An elephant was led across the river below Blackfriars Bridge. The fair was probably the only bright spot in what was certainly a long, dark, bitterly cold winter. It seems magical.
Old London Bridge was demolished in 1831 and replaced with a new bridge with wider arches, allowing the tide to flow more freely. The loss of the old bridge effectively ended the traditional Frost Fairs.
A few years ago I read a book The Frozen Thames by Helen Humphreys. She wrote little vignettes, one each year the river froze. Some are about rulers and some are about paupers. They all felt the cold and saw the magic when anyone could walk over the water.