Portugal, the late 1990s, and I am an undergraduate archaeology student. We are doing an emergency excavation in the countryside, between Porto and Lisbon. An emergency excavation is when there is a small window of opportunity to excavate a site before something happens to it. In this case we were excavating on a hillside before a motorway cut through the hill.

We sleep in a local school gymnasium, on mats on the floor. Before dawn the professor turns on the lights — big industrial lights that hum loudly and grow brighter as they warm up. There is no way to stay asleep through it, but every morning is a struggle. We drink tea or coffee from table, have a quick cold shower in the changing rooms, and grab a bread role before piling onto a bus.

We arrive on our hillside as the sun is rising. Lined up in a neat row, someone walks along spraying our legs with insect repellent. Then as they first rays of the sun warm our cheeks, a mist of mosquitos rises from the grass and buzzes around us, looking for a feed before it becomes too hot.

We are digging a trench across the site. This is a neatly measured line that creates a cross-section of the site. It is a way of seeing what may be on a bigger site without excavating the whole thing. It’s hit and miss, but the best option when you’re short of time.

The trench is one meter wide, and 12 meters long, marked out by taught white string tied to metal stakes in the ground. There are 12 of us, and we each have our own square meter of ground to work on.

This type of work is very intimate. You get to know your little square very well. Over two weeks you cut away the top soil and grass, and then scrape off layer by layer of soil, at a rate of about 10cm per day. You use a trowel to scrape, developing blisters on your thumb and forefinger from the repetitive scraping motion. Each time you find a stone tool, bone, or whatever else is buried there, you stop and measure its location in your cube of ground. This eventually creates a three dimensional map of every find.

I guess it’s like fishing. Some days are boring. You sit in the heat, the dry dirt sticking to your sweat; you scrape and clear the soil and find nothing. But then something happens. Things that are exciting include, obviously, finding a stone tool or artefact. But also exciting is when the texture of the soil changes. If it becomes harder you may have reached an occupation layer, where the soil was compressed by people thousands of years ago. Or it becomes suddenly softer in just one spot, which may be a post hole.

A post hole is where a wooden post was driven into the ground. Sometimes the post is partly intact, but more usually the post decays and soil from higher up falls down to fill the hole, so the density and texture of the soil is different to the touch.

And then you stop for lunch.

We sit around in the shade of trees or rocks, finding something to lean on whilst we eat a sandwich, drink water, and then lie down to sleep a bit. You rapidly get used to being very dirty. Soon you are comfortable lying on the ground under a tree, your head on your bag, or on a rock softened by the wind. When you need the toilet you walk off out of sight, dig a hole, and then after filling it back in, leave some toilet paper on a stick to warn anyone else who also thinks that is a good secluded spot.

Back at work, you listen to some music as you scrape more soil. Soon it is too hot to work, so everyone packs up their tools, tidies the site, and we slump into the bus, leaning into the open windows to catch a breeze, dozing as we bump across the countryside back to what we now gratefully call home. A cold gym floor is welcome after the heat and dirt. After another rest in the cool darkness we sort and wash finds, drawing and photographing, and then we go for a swim.

After 13 of our 14 days we have found a lot. The site slopes down the hill. At the bottom of the slope we found a change in soil texture that reveals what the trained eye can see is an ancient river bed. Along the bank we find small flint flakes, disposable tools used for made quickly to cut something. We think people sat there fishing.

Further up the bank a mysterious single line of post holes tells us that these people had put posts into the ground along the edge of the hill. In our trenches we find more sophisticated stone tools, made with more care and sharpened for repeated use. A stone tool that clearly looks purposefully made is called a flake if there is no evidence it was used. If it has been sharpened, giving it a more serrated edge along one side, it is a blade. This was evidently used, blunted, and sharpened again so we know for sure it was a tool.

By day 13, we think this was a Mesolithic fishing site, but we lack any definitive evidence to link the tools to the post holes. Without this we cannot say it was a Mesolithic site. It could have consisted of Iron Age, or even Medieval posts, that were coincidentally in the same place as some Mesolithic fishing tools. The line of holes remained a mystery.

On the last day, the weather changed. For the first time in two weeks there was a refreshing light wind blowing over the peak of the hill, down towards the river bed. I found a new post hole removed from the others, and at a strange 45 degree angle. We sat there, on the crest of the hill, where these Mesolithic people had sat with their tools cutting fish, and felt the wind on our cheeks, as they would have done. We realised that the row of posts must have been some sort of wind shield, and that stray hole, angled up towards that wall would have been holding it up against the wind.

In the last hours of the day, at the bottom of that last hole, I found a blade. And then it was time to stop.

It had been just in time. That blade dated the whole site definitively. When an item that can be dated is found under a structure it provides a terminus post quem, Latin for time after which. For the blade to have been under the post, in that hole, means the post was put in after the blade. This tells us that the post was either contemporary with the blade, or later, but could not be earlier. This, combined with all the evidence, left us comfortable that the posts and tools were associated and this was indeed a Mesolithic fishing site.

We had spent two weeks sitting on a river bank, holding tools that were last touched by the people who made them something like 4500 years ago or more. We had felt the wind pick up, just as they had. On the excavated river bed I picked up a flake that one of them had dropped, or perhaps thrown in.

At this level archaeology is very intimate. You come as close as you can to average, normal people from the past. There is a sense of connection when you pick up a stone that was dropped by a Mesolithic fisherman, as if your fingers touched briefly through time. And it is that freshness of that stone being exactly where it had been dropped that you don’t get when you touch an ancient artefact in a museum. It is a kind of time travel. For a moment you are sitting on a river bank, 4500 years ago, holding a recently used flint blade, thinking about building a shelter in case the wind picks up.

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