Grow Your Own Cropmarks

Archaeologists use clues within the landscape to identify different historical sites that may lie beneath the surface, often with the help of cropmarks. In this activity, young archaeologists can demonstrate this in their own experiment.

Cropmarks develop when vegetation’s growth is affected by the archaeology in the soil. Features such as boundary walls or stone foundations can stunt growth of crops planted directly above them.

The soil above the archaeology does not retain moisture as well and the crops find it difficult to spread their roots. This often means the contrast in crop growth above archaeological features and alongside them, allows the outline of buildings, for example, to be visible from above. Cropmarks are even easier to spot with the help of aerial photography, when the height advantage allows a better overall view of the site.

To grow your own cropmarks, you will need:

A photo showing two plastic tubs, rocks, seeds and cling film

  • A seed tray or plastic/polystyrene food tray
  • Packet of cress seeds
  • Small stones or gravel
  • Compost or good quality soil
  • Water spray or watering can
  • Cling film

I reused a plastic takeaway box, collected some gravel from my drive and scooped some soil from the vegetable box in my garden.

Step 1:

A plastic container with a line of small rocks in the centre.

Use the gravel to build your own stone wall in the middle of your tray.

This made me think of the boundary wall of a Roman camp like Chew Green or perhaps remains of a Roman road like Dere Street. Fill in any gaps in your wall with smaller stones.

Step 2:

A plastic container filled with soil

Cover your stone wall with soil.

Because we have had such sunny weather for the past few weeks, the soil from my garden was quite dry – even dug from deep in the vegetable patch. So I watered it.

Top Tip: – add the soil to either side of your wall first and then cover the top. If you just pour soil on top, you risk demolishing your wall.

Step 3:

A plastic container filled with soil with seeds sprinkled on top.

Sprinkle your cress seeds all over the soil.

Try and disperse the seeds as even as possible so that there are just as many seeds over your wall, as there is on either side.

Use a water spray bottle to spray the cress seeds and help them stick to the soil.

Step 4:

A plastic container covered in cling film.

Cover your tray in cling film.

Move it to a warm space indoors, where there will be plenty of light.

Uncover the tray and water every so often.

Wait for your cress to grow and assess the difference in growth around your wall. Send us pictures of the cropmarks you grow yourself, why not try and replicate a full Roman fort in a larger seed tray and take pictures from above – just like a an aerial survey.

A plastic container covered in cling film on a window sill.

And now the wait begins! Follow our social media channels for more Young Archaeologist Activities, and an update on how my own cropmark is developing!

Find out more about our Young Archaeologists’ Club here: https://www.thesill.org.uk/young-archaeologists-club/