David Harrison's book The Bridges of Medieval England: Transport and Society 400-1800 (Oxford University Press, 2004, 269pp) [amazon.co.uk] is an in-depth investigation of a period which is sometimes sidelined in histories of bridge building. Unlike more recent periods of history, there is simply less written evidence from the medieval period, less knowledge about what was built, by who, when, or for what reason.Harrison's book is a conscious attempt to redress the balance, and to correct misconceptions about a period where the lack of evidence often leads to mistaken assumptions. The book is meticulously researched and referenced, often from primary sources, and builds a surprisingly detailed picture of the extent of bridge-building in medieval England.
The book is divided into three broad sections.
The first is a quantitative survey, considering how many bridges were built, where and when. Harrison's core argument is that historians have grossly underestimated the sheer quantity of bridges built in medieval times, and that in doing so they have misunderstood the organisational and economic capacity of society in that period.
Surveying a range of historical records, the author deduces that there were almost as many bridges in existence in 1250 as there were some five centuries later, and that many of these bridges dated back to Anglo-Saxon times. He also makes the case that most of these bridges were on roads freshly introduced after Roman times, rather than relics from the Roman occupation. If some of the evidence for earlier periods is somewhat tentative, for later centuries Harrison is able to tabulate numbers of bridges in impressive (albeit often laborious) detail.
The story is one of slow changes in transportation in early medieval centuries, with fords gradually giving way to bridge construction, generally in timber (or timber on stone piers). By the later medieval period, the picture changed to consolidation, with fewer new sites for bridges as most rivers were already bridged at key points, and a gradual conversion of timber structures into stone arch bridges. With written sources often sparse or incomplete, there is a great deal of detective work e.g. by considering place-names such as Bristol, first mentioned as Brycgstow in 1063 ("the site of the bridge").
The books's second part deals with the bridges as structures: their form and materials, and methods of construction. Here the evidence is much stronger, as over 200 medieval English bridges survive today. Bridges built elsewhere in Europe often have the same forms from the same periods.
Little information has survived on how medieval bridge-builders designed their structures: writings on the subject only really started in the 16th century, with the first book in English not published until 1772. Nonetheless, the key concern of the medieval bridge builder was clear: how to survive the elements. London Bridge, completed in 1209, was well-known for how it restricted the river flow, resulting in a huge difference in river levels above and below the river during peak tidal changes. Many early bridges had wide piers and narrow openings, and the history of many medieval bridges is one of occasional collapse, damage, and repeated repair and rebuilding.
Vulnerability to hydraulic forces, and to scour, meant that much of the art of medieval bridge building lay in selecting suitable places for the foundations, and suitable foundation construction. Harrison distinguishes between the large spans of the northern uplands (such as Twizel Bridge and Devil's Bridge), relying on rocky ground for support and providing clear flow for torrential rivers, and the often multi-span viaducts of the southern lowlands, often founded on poor ground and supported on timber "sole-plates" or timber piles driven into the earth. The invention of pile-driving was evidently one of the most significant achievements in the development of medieval bridge building.
There is plenty of interesting material here for anyone involved in conservation of old bridges, or just interested in understanding the challenges the bridge-builders faced, and how they were resolved. As well as presenting the factual details, Harrison is keen to address another misconception - that the many reports of problems with bridges indicate widespread problems with the condition of structures. Instead, he argues that bridges were generally well-maintained, with very few out of service at any given time.
The final section of the book is titled "Economics and society", considering costs of construction, and how bridge building and maintenance were funded. The picture here is of a society willing and ready to spend significant sums of money on a bridge and road network which was critical to trade. However, the mechanisms for funding were very different from today.
Funding for construction was generally private, through wealthy lords and landowners. Maintenance was funded in the same way, as well as from charitable donations (including religious indulgences), from tolls, and through legal obligations. The last of these dated to the Anglo-Saxon period, when "bridgework" was a duty required of certain local communities, along with duties to maintain fortifications and to participate in military service. The "bridgework" obligation fell away only slowly, with a gradual process of lifting of these duties as town charters were renewed or legal challenges made. There was an increasing tendency to place obligations onto bodies with a greater longevity than landowners and residents, with a shift towards the English counties following the 1530 Statute of Bridges.
Some bridges benefited from the establishment of an endowment, lands from which the income was to be used for the management and maintenance of the bridge. Two well known examples survive today: the Rochester Bridge Trust, and London's Bridge House Estates.
This book's main flaw is a lack of illustration. There are a few maps, and 27 historic photographs and illustrations of relevant bridges, but it would have benefited greatly from pictorial explanations of the different forms of bridge construction, and from having some of the more detailed information presented more accessibly (e.g. timelines, tables, and charts).
It is not a book aimed at the casual pontist or perhaps even the armchair historian. It is thorough and detailed, and principally addressed to specialists in medieval history, or the history of transport and economics. However, it is a very impressive piece of work, and I think it should certainly be on the bookshelf of anyone who is serious about the history of bridges in England.