In medieval times it was almost unknown for the River Thames to freeze. With the onset of the so-called Little Ice Age, however, such an event became more common; it occurred some half a dozen times during the 1400s and 1500s, and even more frequently in the 17th century.
When frozen over, the normally stolid Thames provided Londoners with a vast, frozen playground. "Frost fairs" were organised on the river, and these vast tented cities on the ice offered all kinds of amusement and refreshment to the local populace.
The first frost fair was in 1607-08; there were others in 1620-21 and 1662-63, but the greatest of all was that of the very severe winter of 1683-84. It is described in a ballad called A Relation of the Merry Pranks played upon the River Thames during the Great Frost, which begins as follows:
I will tell you a story as true as 'tis rare
Of a river turned into a Bartlemy Fair;
Since old Christmas last, there has been such a frost,
That the Thames has by half the whole nation been crossed.
The freezing conditions that winter lasted from the beginning of December 1683 until February 5th, 1684. The diarist John Evelyn noted: "The Thames before London is planted with booths in formal streets, and with all sorts of trades and shops furnished and full of commodities of all kinds.
"Coaches ply to and fro as if in the streets, and there is sliding, bull-baiting, horse and coach races, puppet-plays and other interludes, tippling and other lewd entertainments, so that it all seems to be a bacchanalian triumph, or a carnival upon the water."
In all there were 10 winters in the 17th century when the Thames froze solid, and another 10 occurred during the following hundred years or so. But, as we know, the Thames at London never freezes nowadays.
The average temperature of the northern hemisphere has risen significantly in the intervening years, and it is now a full degree Celsius warmer than it was in the chilly 1600s. Moreover, London is a bigger city than it was then, and some of the heat generated by the extra people inevitably finds its way into the river, decreasing its likelihood of freezing.
The last of the great London frost fairs was in the early days of 1814. It was a tame affair, lasting only a few weeks until the ice gave way for the very last time 187 years ago today, on February 6th that year. There have been many cold winters in the meantime, but never in any of them has the Thames been bridged with solid ice.