Alston Arches, Haltwhistle: Some Observations

Every time I scoot past Haltwhistle on the A69 bypass, I glance over at the famous Alston Arches and wonder at their peculiar form. It's the line of mini archways running through the piers that grab my attention. It is a very unusual feature of an otherwise robust piece of civil engineering. So this week I decided to go and have a closer look.

Firstly, I wanted to get a nice view through those archways - and, yes, they line up beautifully. How very strange:

I took a few more snaps....

(This last one is taken from the opposite, southern end)

(from OS Maps - Alston Arches Viaduct can be seen slightly right of centre) 

The Alston Arches viaduct was built in around 1850 to facilitate the movement of passengers and especially industrial stuff (lead, mainly) to and from, well, Alston. The line leaves Haltwhistle Station and bends gracefully over the River South Tyne, before heading south. It is a thing of beauty, but that line of arches has puzzled historians for decades. For no one quite knows why they are there. It was once assumed that there was a plan to drive a footway/bridge through the gaps for pedestrian/cart use, which is a lovely (and surely unique) concept; but others think it more likely that they were built into the bridge's construction to lighten the structure's weight, which is, after all, only supported by timber piles.

The bridge was finished in 1851, officially opened in November 1852, then half-destroyed by a flood a month later. It was repaired, but the southernmost pier, being completely rebuilt, was NOT provided with a little archway as per the rest of the bridge's substructure. So if the idea was to build a pedestrian walkway through the piers, well, the plan was clearly abandoned following the flood. On the other hand, maybe it was a 'weight thing' - who knows?

There are plenty of info boards and plaques, mind you. As you can see, the viaduct's useful existence didn't last more than a couple of decades, though it hung on for a good deal longer - before finally being closed in 1976:

(click on images to enlarge)

So, yes, the viaduct is now cross-able on foot, to which lofty spot I found myself quite accidentally by a somewhat circuitous route:

(looking south)

A few other observations. Down at river level I noticed that the (concrete?) base over which the water flows was reinforced with what look like lengths of old railway lines:

And I also noticed that inside the first mini archway, many of the large stones on the floor had Lewis holes in them. They were about three inches long and quite crudely made - which made me wonder if they could be repurposed Roman stones. Lewis holes, though, were in use right up until the twentieth century, so maybe not:

Despite my hour's worth of investigative probings, I'm still none the wiser about those pesky mini archways. Wish I was an expert on Lewis holes, too. Still, my curiosity has been satisfied, and it's one more little task ticked off my history bucket list.

Any input from someone who has a better understanding of these things would be greatly appreciated!