A tide is an obsolete or archaic term for time, period or season, such as eventide, shrovetide, Eastertide, etc. When used on sundials the 'tides' were around three hours long, starting at 6am and ending at 6pm, the working day divided up into these four tides.
The Sundial on the south face of the 7th-century Bewcastle Cross is the oldest in Britain. It is at some height from the ground, and is divided by five principal lines into four spaces, the tides, according to the octaval system of the Angles. Two of these lines, viz., those for 9 a.m. and midday, are crossed at the point. The four spaces are subdivided so as to give the twelve-day hours of the Roman and ecclesiastical use. On one side of the dial there is a vertical line which touches the semicircular border at the second afternoon hour. This may be an accident, but the same kind of line is found on the dial in the crypt of Bamburgh church, where it marks a later hour of the day. The sundial may have been used for calculating the date of the spring equinox and hence Easter.[1][2] The Saxon church at Corhampton, Hampshire has a sundial with markings divided into eight three-hour 'tides'.[3] The ecclesiastical day has five divisions, known as the Canonical hours with four three hour tides between. These were marked on the sundials as lines with crosses and indicate Prime at 6 am; Tierce at 9 am; Sext at 12 pm; Nones at 3 pm; and finally Vespers in the evening at 6 am. As mentioned by Bede, the length of hours and therefore the tides, was flexible at this point in history; being dependent on the length of the day as linked to the seasons. Ecclesiastics and secular people would know which 'tide' it was through the ringing of a church bell, clocks being a great rarity at the time. A perfect copy of the whole Bewcastle cross is located in the churchyard of the Wreay Romanesque Church near Carlisle in England.
