Most people in Christian medieval Europe who gave the matter any thought seem to have expected that the end of the first millennium would also be accompanied by the end of the world. However, it is also undoubtedly true that most people in Europe at this time were illiterate and probably had no idea that the year 1000AD (or M AD, if you prefer your dates in Latin) was approaching until they were told about it by their local clergy. Those people were kept busy with the daily business of staying alive.
The Bible had predicted how the world would end - with a detailed description of the battles, disasters and plagues which would precede the descent of the new Jerusalem, from the skies - but somehow omitted the exact date.
Over the centuries, theologians had studied the Book of Revelation, and tried hard to calculate a date. By far the most obvious date was the year 1000 (although this wasn't universally accepted).
However, not unlike the last millennium, where most celebrations began a year early, on New Years Day 2000, people seem to been confused about when the first millennium ended. Not everyone realised that the first millennium actually ended at the end of 1000AD, rather than the beginning.
We're told that huge crowds gathered in Rome and Jerusalem on New Year's Eve in 999AD waiting for the end of the world. These pilgrims were generally from among the wealthier levels of society. Many would gather there again a year later. After all that effort and expense, I suspect that some were probably bitterly disappointed when it didn't materialise.
The Pope (Sylvester II), blessed the crowd in Rome, on each occasion and sent them home. The Patriarch of Jerusalem did likewise. The people went home and got on with their lives.
The events surrounding that millennium in Christian Europe were neatly summarised by the chronicler Rudolph Glaber. Glaber was a monk at the abbey of Cluny, and wrote of the build-up to the first millennium a few years later. He described it thus:
"For it was as if the whole world were shaking itself free, shrugging
off the burden of the past, and cladding itself everywhere in a white
mantle of churches"
Obviously, that wasn't the end of attempts to predict the end of the world. Joachim, the Abbot of Fiore, later calculated that the end would come in the year 1260. In that year, he wrote, the final epoch of human history, "the epoch of the new spiritual order", would begin with a bang. It seems he was mistaken as well.
Holland, Tom: Millennium: The End of the World and the Forging of Christendom, Hachette , 2011