Pork Scratchings, Stone-Age Style – Frank McNally on the Black Pig’s Dyke

With all the talk about hard and soft borders, post-Brexit, an event in Monaghan town tonight may offer light relief. Or perhaps not. Its theme is the Black Pig's Dyke, an ancient and mysterious series of earthworks that stretches around the northern part of Ireland, from Donegal, via Roscommon and Longford, to Down.

But of course, one of the many theories advanced to explain the dyke over the centuries is that it too was a border: a stone-age predecessor of the current one, protecting Ulster from rampaging southern hordes.

The idea was first mooted to a modern audience by John O’Donovan of the 1835 Ordnance Survey, whose maps included the visible markings, allowing them to be linked in a way that local storytellers never had.

But 70 years later, the theory was given wings by an entomologist. A student of butterflies in particular, William Francis de Vismes Kane was an English-born sheriff of Monaghan.

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He was also an ardent unionist.

So in interpreting the sporadic earthworks as remainders of an ancient frontier, much like Hadrian’s Wall, he may have been at least subconsciously establishing an archaeological wing of the anti-Home Rule movement.

He it was who coined the name “Black Pig’s Dyke” to unify the disparate elements. And that and the theory in general caught the popular imagination. But his “joining-the-dots” approach has been dismissed by subsequent archaeologists, depending as it did on filling in the missing 90 per cent of the border with a mixture of natural features (lakes, mountains, etc) and folklore.

A less extravagant explanation was that the earthworks might have been mere localised barriers to cattle thieves along traditional rustling routes. Indeed, the time-honoured Irish tradition of livestock larceny, so long associated with Queen Maeve, has been revived in recent times, in some of the same areas.

But the locations make no sense as military, social, or economic barriers. It may indeed be a mistake to apply any latter-day logic to the thinking of those who dug the dykes (or had their slaves dig them) two-and-a-half thousand years ago.

The excavation may even have been an end in itself: a way for local elites to leave their mark on the landscape. If so, the enormous trouble they went to has been shown little respect by folk tradition. Their work was instead attributed by subsequent generations to the tusks of a demented boar (from Meath), or in some places, to a giant worm.

Anyway, the latest accumulated intelligence on the dyke will be presented at Monaghan's Market House by Aidan Walsh, Siobhán McDonald, Turtle Bunbury, and Cóilin Ó Drisceoil. Admission is free, subject to booking (047-38162). But if you can't be there, you can still read all about the subject on an excellent website, blackpigsdyke.ie.

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Speaking of earthworks dug by the ancients for reasons obscure, Dublin's Royal Canal was the scene of an annual pilgrimage this week when followers of the great mathematician William Rowan Hamilton retraced the steps, from Dunsink to Cabra, of his Eureka moment on October 16th, 1843.

It was on that date, while strolling with his wife, that Hamilton hit on the formula for quaternions: a way of making four-dimensional calculations, to which we owe video games and space travel.

Understandably excited, he hurried to the next bridge – Broombridge – to carve the equation into the stone. And this famous act of vandalism is now celebrated every October 16th in the Hamilton Walk. I didn’t make it myself this year, but am delighted to hear 200 people did, including a sizeable representation of that all-important demographic: schoolchildren.

All right, getting back to earthworks, we do know why the Royal Canal was dug: as a commercial rival to the Grand, which linked the other side of Dublin with the Shannon. But it was very soon rendered redundant. And the ultimate fate of both canals was to become leisure amenities, especially for pedestrians and cyclists.

The Hamilton Walk is one of the more charming events on the Royal’s calendar now. As I only noticed this week, however, it has also added a new punchline to Dublin’s already witty tram network.

In a notoriously loquacious city, at least the northbound Luas red line can be relied on to get the to The Point (eventually). But the tram system's latest terminus is Broombridge, where the depot is now officially the Broombridge-Hamilton. And I don't know if the last stretch of the service, from Cabra northwards, is quicker than elsewhere. Either way, I shall henceforth refer to it only as the Luas Hamilton.