‘You are seeking many things of me who am exceedingly busy, and you send a messenger who presses me too much at his own pleasure’. Writing in 1076, it is unsurprising that Pope Gregory VII was annoyed by a bishop’s questioning.
Only a few months earlier, Gregory had taken the astonishing measure of excommunicating (the first of three times!) Emperor Henry IV. He was simultaneously attempting to implement a reformation of Latin Christianity itself, now commonly known as ‘Gregorian Reform’. It is safe to say that Gregory was indeed a ‘busy man’.
I’ve spent much of the summer looking into what kept Gregory busy, by studying the Register of his letters which is preserved in the Vatican Library. Using new digital techniques that have never been systematically applied before to Gregory VII’s letters, I’ve discovered a few things that might come as a surprise.
A page from the Register of Gregory VII (showing the so-called Dictatus Papae)
But let me begin with the Register itself, and its 389 entries. How can such an important figure have written so few letters over 12 years? Part of the answer lies with the use of messengers, with Alexander Murray noting that it was ‘more remarkable’ when a messenger came with a letter than without one. As a result, although there certainly were some letters that weren’t copied into the Register, it’s likely that the Register is at least broadly representative of Gregory’s correspondence as a whole. 
The process of collecting and analysing the data led to some interesting discoveries even before we started to crunch the results. We noted for instance a probable mistake in the 1920s edition of the register by German historian Erich Caspar. Gregory wrote two letters on the first and fourth of March 1077 from a place Caspar identified as Carpineto, and two subsequent letters on the 21st and 23rd of March from Carpi and Bianello. But Carpi and Bianello are both around 500km away from Carpineto. It is therefore more likely that Gregory was in Carpineti which is only around 50km away and makes more sense travel-wise.
These same entries may also shed light on Gregory’s travel speed. On the 21st of March, two letters are recorded, issued from different locations. The first, letter 16, is written from Carpi, while the other entry is written from Bianello. These locations are approximately 44km apart and so may show us something like the distance Gregory could potentially cover in a day’s journey.
However, things started to get really interesting when we began to work on the data itself. Two key themes that we explored using visualisations are the strategy behind Gregory’s letter sending, and factors affecting this strategy. As can be seen from the map shown below, Gregory’s recipients were far and wide, even reaching areas such as Norway. This matches Cowdrey’s view that the papacy increasingly saw its function as ‘one of world-wide vigilance and activity’.
All the locations that Gregory VII sent letters to
This ‘world-wide’ aspect is demonstrated even more when we map the recipients of these letters onto the ancient Roman road network. While the majority fit on these Roman roads, we can also see that Gregory is communicating with areas not part of the ancient empire, especially in the northern areas of eastern Europe. This visualises Gregory’s personal strategy of making sure the Roman church was ‘in the fullest sense the universal mother’, concerned with Christians ‘whether or not they lived within the boundaries of the Roman empire at the apogee of its prosperity’.
The destinations of Gregory’s letters in red, imposed onto a map of Roman roads at the time.
Another element of Gregory’s strategy is his politics. The historian Cowdrey believed Gregory wasn’t purposefully political, instead acting upon ‘flexible’ values and methods to pursue goals that were at root ‘religious and moral’. Looking at the number of secular versus clerical recipients of his letters supports this idea of Gregory and his strategy. This data shows us that for the large majority of Gregory’s pontificate, the majority of his communication was with clerical figures. At no point did he really try and specifically increase his political involvement with secular figures.
The number of secular recipients and clerical recipients of Gregory’s letters over time
A second dimension of these letters that the data helps us understand regards the factors that determined their sending, notably the issue of travel. In a world where we can send a message thousands of miles almost instantly, it seems alien to think about a messenger carrying a letter over a number of months. This is how Gregory’s letters were delivered however, with 3-4 months being the standard time for a message and reply.
With this amount of time travelling and the method of travel, weather conditions could become an important consideration. This is explored in the two visualisations below. The first one colour coordinates all the destinations of the letters by season, and seemingly doesn’t show any clear trend. It even shows some of the furthest away letters like those in Norway being sent in winter – which at first glance seems to contradict the idea of season being important. However, if we take the figure of 40km per day as an average speed estimate, we can see that by dispatching the letter in December, the messenger could be expected to arrive in Trondheim sometime around the start of March, and after a stay of a month or two arrive back in Rome well before the autumn, thereby
avoiding the Scandinavian winter.
The destinations of Gregory’s letters colour coded according to the season they were sent
And looking more closely, consideration of season seems to have been quite important to Gregory. By examining the average distance letters were sent in each month, it can be seen that letters sent in the months of March, April and May covered the most distance; with those sent in January and February generally travelling the least distance. This suggests that Gregory considered not just politics but also seasons and weather when sending his letters, with implications for medieval diplomacy more generally.
The average distance of the destination of Gregory’s letters according to the month they were sent
A linked issue concerns the average number of letters Gregory sent each month. Looked at in aggregate, it can clearly be seen that Gregory’s correspondence spikes around March and April, before falling off in the summer and rising again as winter approaches. This trend probably reflects the liturgical calendar. Easter would have been an important time for Gregory, and is also when he held a number of councils. February and August were by contrast very quiet times for the papal scribes.
The total number of letters sent by Gregory in each month
The use of data analysis and visualisation can give us an alternative and valuable perspective on sources that have already been extensively studied by conventional means. They shed new light on existing historiography, such as looking at whether Gregory really was a ‘holy Satan’ or ‘political pope’ by looking at the recipients of his letters. But they can also even perhaps open up new avenues to explore, such as how earthly limitations like seasonal travel may have played an important role in how figures like Gregory VII conducted business. The use of these tools can open up an array of possibilities that would greatly benefit any field of history.
George Litchfield is an undergraduate student at Sheffield. The project Mapping Pope Gregory VII’s letters was supervised by Dr Tom Stafford and Dr Charles West.
Link to the dataset and expanded overview this article is based on: https://doi.org/10.15131/shef.data.12781049
 H. E. J. Cowdrey, The Register of Pope Gregory VII 1073—1085: An English Translation (Oxford, 2002), p. 208.
 Ibid., p. xi.
 Norman Tanner [Review], Reform and the Papacy in the Eleventh Century: Spirituality and Social Change (Manchester, 2005), by Kathleen Cushing, The Heythrop Journal 48.2 (2007), pp. 293-94.
 Alexander Murray, ‘Pope Gregory VII and His Letters’, Traditio 22 (1966), pp. 176-77.
 Cowdrey, The Register of Pope Gregory VII 1073—1085, p. xii; Murray, ‘Pope Gregory VII and His Letters’, p. 163.
 Cowdrey, The Register of Pope Gregory VII 1073—1085, pp. 224-229.
 H. E. J. Cowdrey, Pope Gregory VII, 1073–1085 (Oxford, 1998), p. 10.
 Ibid., p. 2.
 Ibid., p. 2, 86.
 Murray, ‘Pope Gregory VII and His Letters’, p. 168.