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Early medieval Irish watermills

1: Introduction
2: Design
3: Chronology
4: Context
5: Conclusions
6: Bibliography
7: About the author


There are several designs of mill that we have found dating to Early Medieval Ireland. Their chronology will be discussed shortly, however even without this we can still gather much information about the intensification of the economy at this time. Their very existence and role in increasing the efficiency of grain processing shows that more grain was being produced to fit a need greater than there was previously (Rynne, 2003, p. 15).

Reconstruction of Medieval Irish horizontal watermill
Reconstruction of medieval Irish horizontal watermill – The mill is at the Irish National Heritage Park, Ferrycarig. Its design is based on results of an archaeological excavation at a 9th-century site at Cloontycathy. Photo by Niall Roberts

The most common watermill was the horizontal mill (McCormick et al., 2011, p. 39). This sat next to and was fed by a stream (or ‘race’) in which a horizontal waterwheel made of wooden paddles was set (Ó Cróinin, 1995, p. 97). The wheel was connected by a vertical shaft and a hole through the floorboards and middle of the bed stone (which sat fixed to the floor) to the runner stone which would then rotate as the water turned the waterwheel below (McErlean & Crothers, 2007, p. 12).This would grind the corn into flour. This design was simple and required no gearing. It did however need a carpenter and stone mason to construct (Watts, 2002, p. 67).

This can be illustrated by the example found at Nendrum Monastery, excavated in 1999. This horizontal tide mill proved to be the earliest so far in Ireland, dating from 619AD (McErlean & Crothers, 2007, p. 69). This mill, sealed below its successor, was well preserved and the excavations revealed most of its features (McErlean & Crothers, 2007, p. 25). This example contained a mill pond and mill race with two dams with sluice gates (McErlean & Crothers, 2007, p. 25). However, instead of water feeding the mill coming from a nearby stream it instead filled the mill pond at high tide, as will be discussed below.

Tailrace, Ferrycarrig
Tailrace, Ferrycarrig – The water downstream of the mill. Photo by Niall Roberts

The more complicated vertical mill worked in much the same way, however the waterwheel was set into its wheelpit vertically. This was connected to a horizontal shaft instead and therefore required gears and cogs in the lower floor in order to transfer the motion 90 degrees to the runner stone above (Rynne, 1998, p. 91). This method therefore required gearing so was more complex to both build and maintain, however this was made up for in the increased efficiency and power of the mill as the water hitting the wheel in a downward motion forced the wheel to move faster (Rynne, 1989, p. 27).

An example of this is the vertical mill excavated in Killeoteran, Co. Waterford in 2003. This watermill, dating to approximately the seventh century, was fed by a mill race siphoned from a nearby stream and controlled by a number of dams, and sluice gates, complete with a mill pond (Murphy & Rathbone, 2006, p. 20). Being in a marsh, the wooden planks are well preserved and therefore this site can give us valuable evidence about the construction of vertical watermills (Murphy & Rathbone, 2006, p. 27).

Both of these designs could also be adapted to harness the power of the tides instead of streams and these are referred to as tidal mills. In these instances the water from the high tide was captured behind the mill in a mill pond and was then released at low tide by the power of a sluice gate in order to power the horizontal or vertical waterwheel as the water rushed through the mill race and back into the sea (Rynne, 1992, p. 24). For example, the Nendrum watermills mentioned above were both tidal mills (McErlean & Crothers, 2007, p. 3).

Internal machinery of horizontal watermill at Ferrycarrig
Internal machinery of horizontal watermill at Ferrycarig – Showing the hopper for pouring in the grain and the millstones. The upper (runner) stone is connected by a vertical shaft to the waterwheel below. Photo by Niall Roberts

It was argued by some archaeologists that the horizontal watermill, being the less complicated of the two, was used by peasants for their own consumption of flour whilst the more efficient vertical watermill was used in order to produce a surplus supply of flour (Watts, 2002, p. 63). However Watts has refuted this opinion by pointing out that what the horizontal mill lacked in power it made up for in immediate way in which the coarseness of the flour could be changed (2002, p. 63); due to their lack of gears it was easy to alter the space between the millstones which would change the coarseness of the flour. This would not have been nearly as easy to do with a vertical wheel because of its more complicated gearing. Therefore it is entirely plausible that the horizontal watermill was used in the production of surplus flour and therefore was used in the intensification of the Irish economy as it was just as useful as the vertical watermill.

This is further supported by the repeated discovery of rotary querns both on mill sites and elsewhere (Edwards, 1990, p. 63). If peasants were using horizontal mills in order to only grind their own corn rotary querns would be redundant. However, their contemporaneous presence at mill sites suggests that their use was domestic whilst their water powered counterparts were being used to produce predominantly surplus (Rynne, 2003, p. 15).

The material being used in the construction of watermills can also tell us of their importance to the early medieval economy in Ireland. As was mentioned above it was the preservation of the substantial beams used in the construction of mills that allowed us to complete the master sequence used for tree ring dating. These large oak timbers were notoriously scarce until watermills began to be excavated (Edwards, 1990, p. 52). Therefore we could say that this indicates the importance of watermills, as these valuable timbers were being incorporated mainly into these buildings. Therefore they clearly held importance within the community.

Horizontal waterwheel made for the reconstructed mill at Ferrycarrig, based on that found at Cloontycarthy
Horizontal waterwheel made for the reconstructed mill at Ferrycarig, based on that found at Cloontycarthy. The wheel is just under 110cm in diameter, with 19 spoon-shaped paddles morticed into a 30cm diameter hub. It is shown here stored in wet straw to keep the wood from splitting, prior to installation. Photo by Niall Roberts

It should also be pointed out that by the end of the seventh century regional variation can be seen in the style of mills, particularly in the paddles of its waterwheel, which indicates not only that mills were widespread enough to develop their own regional building traditions but also that there were many millwrights, each with their own style (Rynne, 2003, p. 19). This proof of how widespread mills were fits with the documentary evidence. For example we can see variation in the most fundamental part of the water mill: the waterwheel. An example of a partially preserved waterwheel comes from the Deer Park Farm excavations in Co. Antrim. Here the remains of the hub and also some of the paddles were found, and were likely to have come from a mill nearby (Lynn & McDowell, 2011, p. 398). The spacing of the slots cut into the hub of the wheel suggest that it would have originally had seventeen of eighteen paddles attached. We can see from the surviving paddles that these were rectangular at the back, but spoon shaped at the front in order to catch the water more efficiently (Lynn & McDowell, 2011, p. 398). This design is similar to ones found at Nendrum Monastery, however much cruder than those found at Cloontycarthy Mill and Mashinglass (Lynn & McDowell, 2011, p. 398). Furthermore the way in which the paddles were fixed into the hub of the wheel also vary, in the Deer Park Farm example they were fixed into their slots using wedges, however at the mill at Moycraig they were fixed by pegs placed in premade holes through the paddle and hub (Lynn & McDowell, 2011, p. 398).

Therefore it can be seen the design and existence of watermills in Early Medieval Ireland illustrate, and were vital, in the economic intensification of the country. It has been shown that horizontal mills were the most common, not because they were used by many peasant to grind their own corn, but to create a substantial surplus; watermills would not have been needed otherwise, due to the presence of rotary querns. Furthermore the materials themselves also indicate the value of these mills in the economy of the time, as valuable oak timbers were invested into the building of mills. Regional variation develops over time and we can therefore see that watermills were widespread enough to require more than a handful of millwrights to build and maintain.