If you go to Rome, you might notice Monte Testaccio, a green hill in the middle of the sprawling city.
But what you might not know, is that's no natural hill. Instead, it's an Ancient Roman rubbish dump.
Roman amphorae, the large, pottery pots with pointed bottoms, were mostly recyclable. Those used to store wine and grain could, once emptied, be broken down into shards and reused in making concrete. But those used to store olive oil couldn't be made into concrete, since an important ingredient in concrete is lime, but lime + oil = soap. And you don't want soap in your concrete. Another reason that the oil amphorae couldn't be used is that most oil came to Rome in amphorae now known as Dressel 20 which, due to their shape, couldn't as easily be broken down into useful shards. Also, and this might be the big reason, oil goes rancid very quickly, and clay, being quite porous, is really going to hold that stench. For all these reasons, it was almost certainly easier to dump them instead of reusing them or recycling them.
But Monte Testaccio is more than a dump ground. The amphorae weren't just thrown there. It was carefully engineered, because the Romans loved their engineering. It has terraces, and retaining walls, and everything is anchored in place. Here are the terraces:
In addition, lime was sprinkled over the top to counteract the stench of rancid oil. How successful was it? Well, it probably wouldn't have been a delight to live next door.
It's been estimated that Monte Testaccio contains as many as 53 million olive oil amphorae, in which 6 billion litres of oil were imported to Rome. Towards the end of the 2nd century AD, as many as 130 000 amphorae were being dumped on Monte Testaccio each years, and most of those amphorae held 70 litres of oil. The hill is 35 metres high, with another 13.5 metres under the modern street level.
So if you're lucky enough to be in Rome, remember that there's a lot more to it than the Forum and the Coliseum. Sometimes it's worth taking a look at the trash as well as the treasure.