Medieval Mass Dials Decoded

Peter TJ Rumley


  Simple mass dial with just 4-5 lines radiating below and to the left of the (empty) gnomon hole
  Mass dial at the Church of St Bartholomew in Ubley, Somerset (Photo: Jonathan Taylor; all other photos: British Sundial Society)

Some 3,000 mass, tide or scratch dials have been recorded in the UK. Typically located on the south wall of a parish church, this form of sundial was used to mark the ‘variable’ time of liturgical services in the medieval world. This article will consider the various types of mass dial and their origins, where they can be found, and how they were used as timekeeping instruments in the organisation of ecclesiastical and daily agrarian medieval life. Finally it will look at why they went out of use.


The Roman Catholic Church dominated and regulated the daily lives of the people of Britain in the Middle Ages. The Great Rood (a representation of the Crucifixion), stained glass windows and Doom paintings depicting the Last Judgement were potent images that reminded people of their fallibility on earth and the perils of sin.

But the seasons were also represented in church iconography. At a time when the majority of the population could not read or write, visual reminders of the medieval calendar year could be found in the cast reliefs of lead fonts, such as the celebrated 12th-century Zodiac font at St Augustine’s Church, Brookland, Kent. Here, in a series of double arcades one above the other, farming activities are represented below the Zodiac sign for each month as the year unfolds. Life was bound by water, the soil and the Julian calendar.

The cycle of labours and the celebration of cardinal points in the year such as Easter, Christmas and saints’ feast days were calculated by illuminated calendars or medieval almanacs. Such documents were for the exclusive use of the elite. These, too, had richly decorated images depicting seasonal activities such as ploughing, sowing and harvesting.

Medieval society inherited the Julian calendar system, in which dates were reckoned by their relation to three key dates in each month: The Kalends, Nones and Ides, but with variations which made calculations slightly trickier. The Kalends was the 1st day of each month. The Ides was the 13th day of the month save for March, July and October, when it fell on the 15th. The Nones fell on the 9th day before the Ides (counting the Ides day in the calculation). Every day of the month was given a number and calculated backwards from one of the important key days. Thus, in January the Kalends falls on January 1st, the Ides on the 13th and the Nones on January 5th.

  B/w photograph of mass dial with lines radiating in semi-circular formation and engraved with the name Eadric and a small bottonee cross  
  Anglo-Saxon mass dial above the entrance of St Andrew’s Church, Bishopstone, East Sussex bearing the name ‘Eadric’, a 7th-century king of Kent  

While this system determined the date it did not establish the sequence of the days of the week. By manipulating other cryptic letter codes within the calendar, the days were established. Important feast days such as Christmas were highlighted in gold or red (hence the phrase ‘red-letter day’). The important saints’ days had to be reckoned too.

Added to this was the problem of using the 354-day lunar calendar to set the Christian date of Easter, which was celebrated on the first Sunday following the first full moon after the vernal equinox, around 21 March, as it is today. The vagaries of the system meant that there were local time variations across Britain. But how was this religious cycle measured in daily-time?

Perhaps the best known illuminated medieval manuscript of the period is the Très Riches Heures, produced for John, Duke of Berry, between 1412 and 1416 by the Limbourg brothers, which gave the prayers to be said at the daily canonical hours (above left). But it was the Anglo-Saxons who established the measuring instrument for doing so – the mass sundial.


The Anglo-Saxons divided the night and day into eight artificial divisions know in Old English as Tid, or Tides. The four daylight divisions were called morgen, more or less 6am to 9am; undern, 9am to noon; middaeg, noon to 3pm; and gelotendaeg, 3pm to 6pm. Morning, noon and evening are remnants of this division still in use today, as are moontide, yuletide and shrovetide.

Generally, mass dials were about the size of a side plate and consisted of a simple indicator – a short wooden peg or ‘gnomon’ projecting at right angles from a hole in the south wall of a church to cast the sun’s shadow – and a series of scratched or carved lines radiating from the centre point, which the shadow traversed. One such mass dial can be seen on the south wall of the Saxon church (c700) at Escombe, County Durham.

Another example, above the entrance at St Andrew’s Church, Bishopstone, East Sussex, bears the name ‘EADRIC’ (King of Kent, 685-6) and a cross (right). A number of Anglo-Saxon mass dials show evidence of runic inscriptions. Some later examples had Roman numerals indicating the division of hours.

  Diagram showing the medieval canonical hours alongside a common semi-circular scratch dial design
  (Image adapted from TW Cole’s Origin and Use of
Church Scratch-dials, 1935)
  Series of sketches showing the wide variety of mass dial types found in Worcestershire alone (23 designs shown)
  Worcestershire mass dials recorded in TW Cole’s Origin and Use of Church Scratch-dials, 1935

These early timekeeping instruments were used specifically in an ecclesiastical context. Throughout the Middle Ages the church emphasised the reciting of prayers at fixed times during the day, known as the Divine Offices. These canonical hours were known as Matins (before dawn), Prime (6am), Terce (9am), Sext (12pm), None (3pm), Vespers (sunset) and Nocturnes (after sunset). Although by the Norman period the day was divided into 12 hours, it was the significant canonical hours which were emphasised by an extended line with a cross-bar on 8th century dials like the one at St Andrew’s, Bishopstone, East Sussex.

As sunrise at Dover occurred before sunrise at Penzance, the time given was ‘local time’ for each individual church and community, and local variations could occur if the sun did not shine for a few days. Furthermore, a miscalculation could easily lead to a parish priest celebrating certain feasts on different days to a neighbouring parish. It was not until 1880, in response to the complexity of railway timetabling, that British Standard Time or ‘GMT’, was legally adopted in Great Britain.

While it seems a haphazard way of carrying on today, medieval life was planned within the limits of sunrise and sunset. The medieval liturgical and agricultural routines, or those of the household, happily accommodated the inconsistencies.


By the 14th century the appearance of mechanical clocks allowed for a regulated 24 hour time period and ecclesiastical timekeeping was no longer reliant on daylight. The old medieval system was being displaced. The cathedrals of both Salisbury and Wells had clock mechanisms by c1377 (although some dispute this date). The manor of Cotehele in Cornwall has probably the earliest secular turret clock, dated to c1500.

Throughout the 14th and 15th centuries mass dials were still in use alongside the new mechanical clocks. Since most churches were enlarged or rebuilt in this period, it may be difficult to estimate how many earlier mass dials there were.

The later or transitional mass dials are easily recognised as they normally form a complete circle with lines radiating from the central gnomon. They were probably feeble attempts at competing with the 24 hour mechanical clock. The radiating lines in the top half of the circle would not have recorded the time as it would have been night. Why the upper lines of the circle were marked remains a mystery.

As a greater scientific understanding of the relative rotation of the sun to the earth’s axis developed, the true sundial began to emerge, with the gnomon tilted to the true celestial north in relation to the local latitude. Each location requires a different set of calculations and the lines on the vertical sundial were graduated to give an accurate time, as may be seen at the churches of St Michael the Archangel, Litlington, Sussex, and All Saints, Londesborough, Yorkshire. By the middle of the 16th century the mass dial had surrendered to the sundial proper and to the mechanical clock. So too had the liturgy of the church.


Mass dials are generally sited on churches’ exterior south walls to catch the sun. They may be on the smooth cornerstone or quoin of the tower, nave or chancel, above a porch or on door and window jambs. They are normally set at eye level. In the case of St Andrew, Aldborough, Yorkshire, the dial is cut into the window ledge. However, mass dials may be found anywhere on a church even inside the building as at St Peter’s Church, Pirton, Worcestershire. If a mass dial is found anywhere other than the south elevation of a church, this usually means that it has been moved from its original location, often as part of a Victorian ‘restoration’. In such cases the dials were sometimes rebuilt into the fabric upside down, making them unreadable.


The earlier mass dials are, on the whole, of the half-circle type and exhibit a multitude of variations across Britain. Common to all, however, is the central gnomon or peg to cast the sun’s shadow and the ability to show the principal religious services of the day. The basic type would have had a gnomon with three radiating lines giving the time of the services as may be seen with the primitive mass dial at St John Jerusalem, Sutton-at-Hone, Kent, a Knights Hospitaller Commandery. In this case the Terce and Sext canonical hours are shown as the longer lines with the Nones hour not drawn. Similar dials can be found at the Church of St Bartholomew in Ubley, Somerset (above right) and the Church of St Peter and St Paul, Saltwood, Kent.

  Mass dial comprising concentric circles and radial lines with later addition of bevelled sandstone frame  
  Mass dial at the Church of St Peter and St Paul, West Clandon, Surrey, which has been marred by the addition of an inappropriate stone frame  
  Mass dial incorporating a replacement section and with the number four rendered as 'IIII' instead of the conventional 'IV'  
  Repaired mass dial with Roman numerals (including an unconventional rendering of the number four) at the Church of St Mary, Marston Moreteyne, Bedfordshire  

Many medieval churches had their exteriors whitewashed, as were the castle keeps of Harlech, Rochester and the White Tower, Tower of London. In these cases the mass dials would have had their carved lines over-painted.

The range of mass dials is extensive and the designs reflect the knowledge of the individual parish priest in their varying complexity. The British Sundial Society now keeps a register and supplies mass dial recording forms on its website (see Acknowledgements).


Mass dials are delicate pieces of sculpture of great archaeological and historic importance. They are vulnerable to all the problems associated with solid masonry walls, from erosion and plant growth damage to graffiti and vandalism. Most are now weatherworn after centuries of exposure to the elements, and the markings are often only faintly discernible.

The conservation of mass dials varies according to regional geology. An acceptable conservation scheme for soft southern chalk would clearly be inappropriate in a sandstone, limestone or granite district.

In all cases expert advice should be sought through the conservation architect appointed by the church (usually the diocesan advisory committee). A full condition survey should be carried out, including drawings, a photographic record and a written report to justify any physical intervention.

The comprehensive written report should consist of a full scientific analysis of the treatment required. The nature of the stone should be studied in detail with samples taken from an adjacent stone to establish its petrology and determine the most appropriate conservation approach.

Sensitive care and judicious intervention may extend the life of the carving. Nevertheless, however much care is taken to ensure the survival of precious historic mass dials, they will eventually weather to dust if left exposed to the elements.

Ideally an accurate three dimensional digital record of the carving should be made before it is too late. These may be kept as a record of what was once there, but they can also be used to create a replica when necessary. The question is: at what point in the deterioration cycle is it acceptable to move the remnant for safekeeping, perhaps inside the church, and replace the original with a facsimile?



Recommended Reading

TW Cole, Origin and Use of Church Scratchdials, Hill Bookshop, London, 1935

A Cook, Mass Dials on Yorkshire Churches, British Sundial Society, Crowthorne, 2008

AR Green, Sundials: Incised Dials or Mass-clocks, Society for Promoting Christian Knowledge, London, 1926

D Scott and M Cowham, Time Reckoning in the Medieval World: A Study of Anglo-Saxon and Early Norman Sundials, British Sundial Society, 2010

G Zarnecki, English Romanesque Lead Sculpture, Alec Tiranti, London, 1957



Historic Churches, 2013


PETER TJ RUMLEY MA DPhil MA FSA MIfA is an art and architectural historian, consultant historic buildings archaeologist and conservationist.

The author would like to acknowledge the assistance of Tony Wood of the British Sundial Society.

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