Re: Nobody is quite sure what it was originally built for.
Dunwich doesn't really have anything to do with global warming
Sorry, that was me being sarcastic.. And also didn't help the other grand city of the Eastern Angles, Norwich.. Which also succumbed to the combination of longshore drift and North Sea storms & surges. Nowadays, this is naturally blamed on global warming rather than normal hydrological processes.
At one point, the River Alde came out at Aldeburgh, now it comes out ~12 miles away. Wikipedia has a nice map with points showing the lengthening of the spit over time.
Yup.. But there were also human factors, ie when rivers ceased to be as useful for trade & transport, they weren't maintained as well leading to nature taking it's course and silting. A bit like the Lord's Deben, which is far less navigable than it was when I was a kid. And then of course there's modern land management thinking that restoring wetlands is a good thing, even if that increases flood risk and related issues like the ague..
Also I think some of the changes to the Alde were down to the MoD pulling out, so sea defences not being maintained.