How To… Mark Out The Perfect Trench

So you thought you could forget about Pythagoras and his Theorem? Think again.

It turns out that junior school geometry you never thought you’d never need again is key to marking out the perfect trench. Here’s how to do it…

You will need:You Will Need

  • 4 x Pegs
  • 2 x Open Reel Tape Measures
  • Brightly coloured string
  • A calculator (or someone very good at mental arithmetic)

Step 1: Decide where to place your trench

Step 1

First up, decide where you’re going to place your trench – Joan seems to have found a good spot within the Leiston Abbey refectory.

Situated close to a culvert, it’ll help us answer some important questions about how water was moved around the site, as well as investigate some local legends (word has it one of the culvert tunnels leads all the way to Dunwich!). From a management point of view it’ll also help us assess the extent of damage to the abbey from burrowing bunnies!

Step 2: Time for a maths refresher


Just when you thought you could forget all the geometry you learnt at school, setting out the perfect trench requires the use of Pythagoras’ Theorem: a2 + b2 = c2.

We want our trench to measure 2.5m x 2m, and to make sure we get the PERFECT corners (90◦ angles) the diagonal needs to measure the square-rooted sum of the two sides squared and added together i.e. 2.5m2 x 2m2 = 10.25,  the √10.25 = 3.2m which gives us our diagonal… still with us at the back of the class?

Step 3: Mark it out on the ground

step 2

To mark this out on site, start from a fixed peg representing one corner of the trench and attach a tape to the peg. Measure the tape out to the length of side ‘a’ and place another peg.

From this peg attach another measure. Extend both measures out and bring them together so that they cross at the desired length of both ‘b’ and ‘c’ and place another peg. Repeat the process for the final corner.

Now you’ve got the 4 corners of your trench, mark it out by attaching a length of string & between all four nails to create a square or rectangle. It’s a good idea to make sure the string is highly visible to reduce the risk of people tripping over it; we’ve opted for a fetching orange.

Step 4: Remove the topsoil

Ben removes the topsoilFinally, you can start removing the top soil! Et voila! You have a trench that’s ready to dig… and in this case, you can already see just how much damage those bunnies have done.

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Written by Rosanna Ring

Rosanna is one of DigVentures' intrepid Community Archaeologists. She's busy turning Barrowed Time (our dig at Morecambe's Bronze Age burial mound) into a real seaside adventure, and getting the Pop-Up Museum on the Prom ready for you to visit!

Read more from Rosanna Ring +

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