Roman Wall EarthCache

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About the Roman Wall

Just north of the Tower of London stands one of the best surviving sections of London’s ancient Roman wall. Built around AD 190–225, this huge structure once marked the eastern boundary of Londinium. Originally over 6 metres tall and more than 3 kilometres long, the wall was built for defence and remained important through the medieval period and beyond.

What makes this part of the wall special is how it showcases different building phases, utilising various types of stone — some Roman, some medieval, and some reused from other structures. It’s a perfect example of how ancient builders used local geology, trade routes, and even recycling.

What is Kentish Ragstone?

The main stone used in the Roman wall is Kentish Ragstone, a grey-green, hard limestone quarried in Maidstone, Kent. It was transported by barge up the River Medway and the Thames to build many Roman and medieval structures in London. It’s tough, resistant to weathering, and full of tiny fragments of marine fossils. It is important to note that there is very little accessible hard rock in South-East England due to overlaying sedimentation.

Kentish Ragstone comes from the Lower Greensand (Hythe Beds), formed in the Early Cretaceous. It appears in layered bands with hassock, a softer sediment. When freshly quarried, it’s grey-green, later weathering to browns and yellows. Its durability and colour made it popular for centuries in building iconic structures like the Tower of London and Westminster Abbey.

Reused and Recycled Stones

Look closely — not all stones are the same. Some sections of the wall include:

• Brick fragments reused from Roman buildings
• Limestone or tuff blocks from earlier or distant structures
• Mortar and rubble cores between outer faces
• Shells and quartz grains

This mix of materials is a visible record of urban recycling that’s been going on for nearly 2,000 years!

Weathering and Preservation

Compare how the stones have weathered over time:

• Ragstone is often pitted but retains its shape
• Softer stones erode faster, showing gaps and worn edges
• Modern repairs look cleaner or smoother

These differences let us observe natural and human influences on ancient stonework, like pollution, acid rain, and biological growth (lichens, mosses).

Fossils in Ragstone

Although large fossils are rare, Kentish Ragstone contains tiny shell fragments from marine life. If you look closely, you might see:

• Bivalves – shellfish with two valves, like clams or oysters
• Gastropods – spiral-shelled sea snails

These fossils provide evidence that the stone formed in a shallow marine environment during the Early Cretaceous period.

Examples of Weathering

Here are examples of different types of weathering that you may observe at the Roman Wall:

Physical weathering – freeze-thaw cracks and flaking stone:

Chemical weathering – pitted surfaces and black crusts due to pollution and acid rain:

Biological weathering – moss, lichens, or root growth breaking down stone:

Logging Tasks

Please send your answers within two days. If not received, your Found It log may be deleted. You may log a Found It before receiving a reply. Use the “Message this owner” button or the Message Centre.

1. What is the colour of the Kentish Ragstone?
2. How would you describe the texture of the Ragstone? Is it smooth, rough, pitted, or layered?
3. Describe any visible fossils or grains in the Ragstone. Look for: tiny white or pale spots, shell fragments, spirals, or rough and grainy textures.
4. Find another type of stone (e.g. reused brick or tuff). What does it look like, and what might its original purpose have been?
5. Look at two different sections of the wall. Which shows more weathering? Describe any signs such as blackening, erosion, or cracks, and match them to the types of weathering (physical, chemical, biological).
6. Why do you think the Romans chose Kentish Ragstone as a building stone?
7. What does the mixture of building materials (original and reused) tell us about Roman and medieval construction and trade?
8. Take a photo of yourself or a personal item, such as a name card or your GPS, near the Roman wall. Please don't include close-ups of specific fossils or stonework in your public log.