Mounds are an odd one. I'm just reading the excavation report from a mound in Drimnagh, Dublin. Despite being 40m in diameter this wasn't even marked on the 1837 OS maps, so it was assumed to be modern(ish) when it was threatened by quarrying in the 1930s.

What they found was extraordinary and totally unique. It was a mound over a mound. The 30m diameter inner mound was of burnt sod and tree trunks. Up the centre of it was a stone chimney. An air intake led from the outer edge to the centre below the mound. When alight and blazing away flames would have shot out of the top!!!! A unique bowl was found in the mound too - the only (approximate) parallels coming from Spain. Was this a manmade symbolic volcano? A beacon? A kiln? No broken or part fired pottery was found in this context. The inner mound was dated to around 2000bce, but this date is crap and must be pushed back due to later finds elsewhere. A piece of Windmill Hill Ware was found on its surface.

The outer mound was LBA and layered in a similar fashion to Knowth. Two burials were sunk into the top of the mound and an cinnery urn had be placed on the top of the inner mound before the outer mound was thrown over the inner one.

There are at least 30 unexplored mounds in Co. Dublin. How many of them hide similar things?