Architecture is supposed to be permanent, but take a good look around you, and ask yourself if the house or building you're in will be around in a thousand years. We have access to better materials science than the Romans did--well, except for concrete--yet the architectural evidence of their existence will likely outlast ours. (Our mark will be that we screwed up the environment.)

Now a combination of environmental conditions is revealing long-forgotten Roman structures. An unprecedented drought in Wales has revealed ghostly outlines in the earth, visible from above:

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So what's going on here? As reported by the Royal Commission on the Ancient and Historical Monuments of Wales, here's precisely what we're seeing:

"Newly discovered cropmarks of a prehistoric or Roman farm near Langstone, Newport, south Wales."

"The 'playing card' shape of Pen-llwyn Roman fort, Ceredigion emerging in parched grassland."

"The almost ploughed-down medieval castle mound at Castell Llwyn Gwinau, Tregaron, showing clearly under parched conditions."

"A newly discovered Roman fortlet near Magor, south Wales, emerging in ripening crops."

"The Iron Age hillfort of Gaer Fawr near Lledrod, Ceredigion, looking across the parched landscape of mid Wales."

"The buried ramparts of Cross Oak Hillfort, Talybont on Usk, showing as cropmarks."

"Extensive cropmarks of Trewen Roman farmstead or villa, Caerwent, south Wales."

The presence of the visible outlines has to do with the construction methods of ancient fortifications. These illustrations below show how moats and defensive walls, once reclaimed by nature and modern farming, still leave telltale traces:

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Next we'll look at how we modern-day earthlings do the exact opposite--building tall, impressive structures that we eventually demolish, leaving nothing behind for future archaeologists to find.