Currency Bar Plough

Crew Type (“Currency Bars and other Forms of Trade Iron,” Peter Crew):
L (Maidenhead): Thick blades of variable length with short winged sockets, some with flanged edges. 750-785 x 40 x 6-8mm; 930-1210g. About 10 known, mainly from the river Thames. 
M (Datchet): Shorter, tapering blades with winged sockets. 540-600 x 44 x 6-8mm; 800-865g. Moderate phosphorus, low carbon metal. About 6 known, mainly from the river Thames. 
N (Llyn Cerrig Bach): Thick blade with welded tip and winged sockets. 620 x 32 x 7mm; 820g. Low phosphorus metal. 4 known from lake deposit, north Wales.
P (Park Farm): Long thick blades with heavy sockets. 680 x 40 x 11-15mm; 1036-1451g. 2 known.
Q (Glastonbury Rod): Thin rods with tapering socket. 535 x 20 x 8.5mm; 540g. 4 known from south-west England.
T (Brixworth): Short lenticular blade with heavy socket. 453 x 36mm; 430g. 2 known from Northamptonshire and Oxfordshire.
W (Gransmoor): Short thick bar with long socket and an open weld near the socket end. 420 x 33 x 9mm, 620g. Moderate phospherus, variable Carbon metal.  One known from East Yorkshire.



Around 1500 high-quality, shaped iron bars have been found in hoards in southern Britain, especially around Iron Age hill forts and settlement ditches. Around 400 survive, of which about 120 are complete. They are known as a trade currency of the Iron Age tribes from around 200BC until the introduction of coins around 50 years later (finds at Hod Hill fort, where 27 have been found, suggest they stopped being used as coins were adopted). What appears to be iron bar currency was mentioned in Julius Caesar's Commentarii de Bello Gallico (he may have been referring to iron ring money, but iron bar currency is more likely given the discoveries of bars).

However, while several sites have evidence for the trade of bars of different types and metal composition, their use as currency is only a partial explanation. The findspots at the edges of settlements also suggest they might have been used for the ritual definition of boundaries. Many have been found partially forged into other goods. Some are fragments with chisel-cut ends, having been used for manufacturing bladed objects. Impurities in the metal point to the geographical source of the ore, suggesting the bars were made to demonstrate the usefulness of the local metal as a raw material. 

The form of the bar demonstrated the quality of the iron and its suitability for different kinds of work - bars with sockets were of metal good for forming thin sections, while those with folded tips could be welded by a blacksmith. Since their suitability can be identified by sight, they would have had a predictable value and so were useful as a medium of exchange and a store of wealth. But they were not official currency like coins, issued by a ruler. They were made by local blacksmiths. Rather than simply a currency, the bars were part of a much more sophisticated trade in a valuable commodity.

The bars generally weigh between 300-500g, but there is not a standard range of weights. However, the dimensions, weight, shape and metal composition are closely correlated, suggesting they were regional products smelted from local ores.

There are at least 20 distinctive types, distinguished by their dimensions, the shape of the socket and the welding of the tips. The following are the main groups, roughly associated with the following areas:
- Sword: Hampshire, Dorset and along the Jurassic Way up to the Humber (the Corieltauvi, Dobunni, Durotriges and Atrebates tribes)
- Spit: Cotswolds, Somerset and the Severn Valley (Dobunni and Durotriges tribes). Finds cluster around the Forest of Dean, one of the major sources of low phosphorus iron ore in Britain
- Plough: Thames Valley, Kent and the Midlands (the Corieltauvi, Catuvellauni and Cantii tribes)
- Bay Leaf: a single hoard found in Cambridgeshire (the Corieltauvi tribe)

Spit-shaped bars are the most commonly found (representing half of all finds) followed by sword-shaped (40%) and plough-shaped.

The shape can be differentiated by the hilt: the Sword type is pinched before one end of the bar; the Split type is pinched on the end (and unlike other types, often does not narrow significantly with length); the Plough type has raised flanges at one end; and the Bay Leaf type has a long pinched area, making it resemble a leaf.

See also “Offering from the River”, Chris Rudd.