Roman Groma Surveying

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Blackadder43
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I was watching a youtube video earlier on Watling Street, and part of it showed how the Romans made their roads so straight with a basic set of poles and 2 people, the surveyer and his assistant
But then they showed how they made the exact crossroads linking off from the main road

They used an instrument called a Groma
https://en.wikipedia.org/wiki/Groma_(surveying)

This got me thinking because we often see Roman steelyard weights identified, but i couldnt remember anyone identifying a "Groma" weight
So i looked on the PAS database and there were only 5 entries that used the word Groma in their description
Yet, there are pages and pages of "steelyard weights" :shock:

Could some of those be Groma weights?
There would have been thousands used i imagine with the network of roads that the Romans built using this tool

I suppose it is nigh on impossible to distinguish between the 2, but it does show that the identifications are possibly not always correct for these weights we find

Just thought i would think out loud, but it was fascinating to see the tools they used, and how their knowledge was lost for a few hundred years whilst our country was in a bit of turmoil
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Saki
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Thats actually very interesting.
I am always amazed too at how much "knowledge" of items, things, customs etc. we seem to have lost
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Oxgirl
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That is interesting! I think we misidentify loads of stuff. After all, as an example, how many pot mends were there? I bet there’s loads of things that we take the easy route of assuming it’s the same as the last misidentified item. I guess weights were used for lots of things so knowing exactly what is hard!

Love the new knowledge though :thumbsup:
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Pete E
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Blackadder43 wrote: Mon Nov 30, 2020 10:06 pm I was watching a youtube video earlier on Watling Street, and part of it showed how the Romans made their roads so straight with a basic set of poles and 2 people, the surveyer and his assistant
But then they showed how they made the exact crossroads linking off from the main road

They used an instrument call a Groma
https://en.wikipedia.org/wiki/Groma_(surveying)

This got me thinking because we often see Roman steelyard weights identified, but i couldnt remember anyone identifying a "Groma" weight
So i looked on the PAS database and there were only 5 entries that used the word Groma in their description
Yet, there are pages and pages of "steelyard weights" :shock:

Could some of those be Groma weights?
There would have been thousands used i imagine with the network of roads that the Romans built using this tool

I suppose it is nigh on impossible to distinguish between the 2, but it does show that the identifications are possibly not always correct for these weights we find

Just thought i would think out loud, but it was fascinating to see the tools they used, and how their knowledge was lost for a few hundred years whilst our country was in a bit of turmoil
I think you might be onto something....To add a bit more credence to the idea it should be noted that the Romans also used another survey device called a "chorobate" to find levels and plot slopes ect, and these too used a number of plumb bobs to get true verticals....

It makes you wonder what else these lead weights could have been used for...
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Easylife
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It's a tough call to date any lead weight with any great accuracy. Some may look older but most seem much newer. It's probably fair to say that generally a lead weight is no older than coins or other artifacts found on the same site. I mean what are the chances of finding a single Roman steelyard weight when the area is totally void of Roman coins and artefacts? 🤔
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Steve_JT
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Thanks for the info, interesting article :thumbsup: :thumbsup:

I will do some research as it’s such an interesting subject

Difficult to call with any certainty any lead weight, even lead whorls, as said if your finding Roman to modern could be any date range

The Roman technology would have been used by others no doubt going forward to mark out lots of things through the ages, weights used for a hundred and one different things

I tend to record whorls with a wide date range from Roman to post medieval and put something in the notes section for the FLO to call it as to what age

Steve
A foolish faith in authority, is the worst enemy of truth." Albert Einstein
Pete E
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Easylife wrote: Tue Dec 01, 2020 1:14 am It's a tough call to date any lead weight with any great accuracy. Some may look older but most seem much newer. It's probably fair to say that generally a lead weight is no older than coins or other artifacts found on the same site. I mean what are the chances of finding a single Roman steelyard weight when the area is totally void of Roman coins and artefacts? 🤔
I found my Fibula on a site that was devoid of any other Roman finds, so it does happen but I get what you mean...

Also, If the weights are lost in transit, that is likely to explain why there are few other finds of the same era???

That said, I had a look at the PAS records, and it seems that most of the few weights attributed to being from a Groma were quite elaborate cast copper alloy affairs...

We would need the input from a Roman expert, but perhaps lead was not the favoured metal for these plumb bob weights used in surveying equipment?
Dave The Slave
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Very interesting post, Mr B.
Have often seen steelyard weights posted but not really looked into their purpose, not found one as yet.
Now have a better understanding of both uses.
Cheers, :thumbsup:
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Pete E
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I found this weight a while back, but have been unable to get it dated with any certainty...The tiny patterns look like vegetation suggesting it had been crudely cast in the ground but other than that I have no idea about it....
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coal digger
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You have to be open minded also when those so-called steel weights could be part of the military plumbata. These were in many forms and sizes and designed to harass the enemy.
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figgis
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Fascinating stuff, Bruce. Please hold back 2lb of jellybeans from what's owed me by way of showing my appreciation :thumbsup:

Yep, lead has been used for various purposes for a lot of years, and sometimes the same form for the same purpose spans many centuries. Dating lead is nigh impossible and any white patina isn't necessarily a sign of antiquity so you can't go by that, either.
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Easylife
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The actual weight of a lead weight may give some clue corresponding to the weighing system used at the time taking into account some wear and tear, but then again maybe just a very crude copy from a different time period? 🤔
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