Why Archaeologists Love Digging Up Privies

Post Date: 

Wednesday, May 20, 2015

by Anson Kritsch, University of Iowa Office of the State Archaeologist

So what is a privy?

You may know it by a different name: head, john, latrine, lavatory, outhouse, potty, restroom, the can, throne, washroom, water closet... Simply, a privy is an outdoor toilet. Before you hurl back in disgust, let me explain why privies are so interesting to archaeologists. You may already be privy, wink wink, to the fact that archaeologist are interested in people’s trash. But, a person’s toilet is an entirely different kind of trash. This is precisely why we love privies.

One reason we love privies is that people throw their trash in them. Back before the days of municipal trash pickup, people had to get rid of their own trash. Sometimes this meant hauling your trash to a local ditch, but that could be cumbersome. One very close and very convenient place to throw all your crap is, well you know... I think you get the idea. Things like broken plates, glasses, lamp chimneys, smoking pipes, your sister’s favorite porcelain doll (see Figure 1), and heck, even old rusty tin cans tell us about the people that used the privy as well as roughly how old the privy is. 

Anson Kritsch holding a white ceramic girl doll found in the privy
Figure 1. Anson Kritsch holding a white ceramic girl doll found in the privy.

Also, people go to the bathroom in privies. Wait, why is THAT important to an archaeologist? Really it boils down to two things. First, it tells us about a person’s diet. Just like how the broken plate can tell us how old the privy may be, a chicken bone or peach pit tells us what they were eating. Second, it tells us about seasonality of use. Now hold on, how can you tell the season of use? Easy -- seeds. You probably are aware that the body cannot break down everything you ingest. One of those things is seeds. Seeds come from fruits and vegetables. Fruits and vegetables are grown during certain times of the year. Thus, if we have seeds from, say a strawberry, and we know that strawberries are harvested in late spring to early summer, we can say the privy was used in late spring to early summer. And that is not even the best part.

You see, as a privy fills up it creates layers of dirt, peoples trash, and well you know… fecal material (see Figure 2). Archaeologists excavate each of these layers separately and collect the artifacts separately. The artifacts and the seeds (or lack of seeds) tell us how old each layer in the privy is, as well as what the people were like. Now this is all well and good, but I know you are wondering... how do we collect the seeds? 

A privy feature from the School of Music excavations at the University of Iowa
Figure 2. A privy feature from the School of Music excavations at the University of Iowa

Flotation

While we are digging these discrete layers of a privy, we collect a sample of the dirt in a bag. Later, we will put this dirt in a machine full of water and agitate the dirt. This is called a flotation sample. As the dirt is agitated in the water, floatable material comes to the top and is collected. The non-floatable material sinks to the bottom and is also collected. Simply, what floats floats and what don’t don’t. In the case of privy material, things like porous bone and seeds will float to the top and dense plates and glass will sink to the bottom. Check out the video below to see a flotation of night soil in action! 

So, hopefully you got an education of why privies are so important to archaeologists. Basically, they are like time capsules that allow us to look into the past with great clarity, a luxury archaeologists rarely get. So what do you think? Would you dig a privy? Was this interesting? We'd love to hear your perspectives and ideas! 

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