Why is pottery from the Early Middle Ages difficult for archaeologists to find?

Listen to part of a lecture in an archaeology class.
Professor: In our last class, we discussed technologies, like radio carbon dating and digital imaging, that help us interpret archaeological evidence, We looked at some of the challenges of drawing conclusions from the available evidence. One example I want to mention has a strong impact on our ideas about the population size of ancient settlements, in particular in Western Europe during the period known as the early Middle Ages.
    The Early Middle Ages, from roughly 500 CE to 1,000 CE, refers to the period in Western Europe following the fall of the Roman Empire. You’ll probably remember, the Roman Empire was the major world power about 2,000 years ago. At its height, it included all the land around the Mediterranean Sea and extended as far north as, well, the island of Britain, and Roman sites have been easy for archaeologists to find. There are ruins of huge buildings, like the Colosseum in Rome or even entire cities like the ruins of Pompeii, just south of Rome, and when we look across the expanse of the empire, the evidence shows a landscape that was densely populated.
    In addition to the obvious remains, the huge public buildings and monuments, we also observe countless remains found in private buildings, like statues, decorative artifacts, shards of pottery, but then there’s a sharp decline in the amount of archaeological evidence that dates from the Early Middle Ages. From this picture it’d be tempting to conclude that there was an equally sharp decline in population, but let’s look again. As we said, the Romans left behind countless long lasting remains, items made of materials that were strong and durable. Roman houses, for example, were made of mortar and cement with tiles for the roofs, but in the Early Middle Ages homes were made of organic materials, mostly wood, and they had thatched roofs, simple structures of straw and mud. Materials like these decay over time, so naturally that makes it difficult to find these sites.
    Another reason Roman sites are so much easier to locate is that even small artifacts are visible. Roman pottery, for example, it was typically glazed, so it’s very shiny, easy to see against the soil, but pottery of the Early Middle Ages was brown or gray, and it wasn’t glazed, so you’d have trouble spotting it at an excavation. It’s kind of camouflaged against the soil, so it’s easy to draw the wrong conclusions about population size based on the available evidence. Let’s compare two sites that were unearthed in Britain: one dating from the Roman Empire, the other from a few centuries later during the Early Middle Ages. The Roman site is called Bradley Hill. This was a farmstead that would have been inhabited by a few families, so figure about 20 people living there. From this one site, we have remains of a tiled roof and other sturdy materials and thousands, literally thousands, of shards of shiny pottery.
    Now compare that with the settlement in Britain from the Early Middle Ages called Oevering. Writings from the period tell us that Oevering was the estate of a regional king, and that it was occupied by over 100 people for more than 200 years. But what’s left of Oevering? Virtually nothing, nothing from the palace, most likely built of wood. ln fact, the only evidence we have of that are the post holes, the holes dug in the earth where the timbers or wooden posts were placed to support the walls and roof, and we didn’t even know about these until aerial photographs revealed markings that weren’t evident from the ground. And this is just one example of how a new perspective, in this case made possible through aerial photography, helped us realize that evidence, or the lack of it, could lead to false conclusions.
    It’s possible, even likely, that there was some decline. What I mean is that the evidence, especially when it’s incomplete or analyzed in isolation, doesn’t tell the whole story. Now all this may not seem relevant to this week’s reading about the ancient Mayan populations in Central America, which we’ll get to in a minute, but you’ll notice that your book includes population distribution maps that have been generated based on archaeological evidence, so a word to the wise: population distribution maps for western Europe show lots of large, empty spaces for the Early Middle Ages, even though evidence like those post holes and documents about Oevering, might paint a very different picture.