Many readers will know where Calvert Street is in Norwich: it runs from Colegate northwards to the inner link road. Before that monstrosity was built, cutting Norwich-over-the-water into two, Calvert street used to stretch somewhat further north than that.

It's called Calvert Street after the distinguished Norwich citizen, John Calvert, who owned a house in the street in the 18th century. Calvert was Sheriff of Norwich in 1741. But it's a very ancient street, so this raises the question of what it was called before Calvert built his house. You can answer this for yourself by walking along Calvert Street and noting that there's a house there, on your left as you head out of the city, called Snaylgate House. The fact is that for hundreds of years before Mr Calvert appeared, the street had been called Snailgate.

That sounds like a pretty odd name, doesn't it. Perhaps it's no surprise that local people decided they would prefer Calvert to Snail. But where did the older name come from? We know that the gate part of the name was simply the Old Danish word for street: that part of Norwich was strongly associated with the ninth century Danish invasion and subsequent settlement. (The Cole in nearby Colegate may be from the Scandinavian man's name Koli.)

But why snail? Well, the name may quite simply have derived from the fact that, at some early period, there were lots of snails to be found there. But it could also be that a family lived on the street whose name was Snail – that was a known surname, originally applied to people who were rather slow…

Interestingly, though, there was also a period of time when the street was known as Snackegate. Prof. Karl Inge Sandred, the expert on Norwich street names, calls this a 'corruption' of Snailgate. But it is not easy for a linguist to see how this could have happened. Why would speakers stop saying snail and start saying snack

I wonder about another possibility. The Snackegate name is first recorded as being used in 1620; and one thing we know about Norwich at the beginning of the 17th century is that the city was full of refugees, the Strangers from the Low Countries who at one point formed nearly 40pc of the population. Dutch and Belgian experts tell me that one of the words for snail found in older Dutch dialects was snek.