LENT RUNS FROM midday on Ash Wednesday to midnight on Holy Saturday, the day before Easter Sunday.  For Catholics, it ends two days earlier, at midnight on Maundy Thursday. The ‘forty days’ of Lent commemorate the forty days that Jesus (and before him, Moses) spent fasting and praying in the wilderness, but the Sundays don’t count because you aren’t supposed to fast on them.

The technical term for the period is quadragesima, Latin for ‘fortieth’. In the late Middle Ages, when preachers in Britain began using English instead of Latin, they cast around for a simple but appropriate word to replace it, and fastened on ‘Lent’ – which then just meant ‘Spring’ and was related to the days ‘lengthening’.

The reason why penance and fasting are suspended for the six Sundays that fall during Lent, is that they are considered celebratory tasters for Easter Day, the most important feast of the Christian year.

Some may consider this weak-willed or against the spirit of the thing, but the terms of the Lenten fast have always been treated as if they are negotiable. Even in the 6^th century, when Pope Gregory the Great first came up with the idea of giving up meat, milk, cheese, butter and eggs for 40 days, it was loosely interpreted. The Celtic church advised fasting during the day but having a hearty supper of bread, eggs and milk in the evening. In 10^th century England, Archbishop Aelfric went the other way and took a hard-line approach – banning sex, fighting and fish as well.

In general, though, fish have always been the saving grace of Lent. Henry VIII encouraged Lent to support the nation’s fishing industry. As hungry Christians carried the Good News to distant climes, the definition of ‘fish’ became quite flexible. At various times, muskrat, beaver and barnacle geese have all been officially counted as ‘fish’ – as has the capybara, a kind of giant South American guinea pig that can stay underwater for five minutes. In Venezuela today, it forms a magnificent centrepiece for Lenten feasts: it’s the world’s largest rodent.

Perhaps because of all these shenanigans, or perhaps because fasting implies the value of its opposite (feasting), the English Puritans abolished Lent completely in 1645. More recently Lent is been co-opted into the self-development calendar, billed as a time of self-discovery were we leave behind old ways of being and either ‘root sin out of our lives’ (catholic.org) or ‘challenge our vices’ by stripping out such anti-social behaviour as internet shopping, biting your nails or using plastic bags (detoxinista.com)

And in a time of mounting religious extremism, Lent is even being used as a way of bringing different faiths together. A US movement called #Muslims4Lent is promoting observance of the Lenten fast as a way of demonstrating their solidarity with Christians. Young Muslims are tweeting pictures of themselves holding up signs saying what they will be giving up for the next 40 days. The eclectic nature of their sacrifices, with a slight preference for dairy  – cheese, Taco-Bell, sour cream and onion chips, chicken wings – would have delighted Pope Gregory the Great.

But on the subject of giving things up, the last word should really go to the marvellously dry Catholic writer of detective stories, Monsignor Ronald Knox. When asked what he was giving up for Lent, he replied: “As I don’t drink alcohol, and giving up smoking would be far too serious a matter, I propose to give up Gibraltar: it’s not such a habit with me.”

John Mitchinson is former Director of Information at QI and co-founder of publishing company Unbound

@johnmitchinson