Ancient Sundials

Dialface ID 168

ObjID169-1

Holder:: Soprintendenza Speciale per i Beni Archeologici di Napoli e Pompei, Pompei, Italy
Site:: Pompei, Italy
Material:: Limestone, White
Dating:: before 79 CE
Type:: Cone, Conical
Inventory Number:: 14330
Site Geolocation:: Lat.: 40.7503, Long.: 14.4871

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Abstract

Lead fills the gnomon hole in the top surface of the dial. An 8 mm deep groove with sloping sides connects the hole with the front surface. The eleven hour lines do not continue beyond the winter solstice but continue lightly beyond the summer solstice. These two solstices are always equidistant from each other and from the lower edge. The third, sixth, and ninth hour lines are marked as shown in the plate. A crescent flanked by two six-leafed rosettes decorates the oblique front of the dial below the shadow-receiving surface. A half-cylinder molding separates this decorated face from the sloping base. Construction guide lines remain on the right side of the dial as shown in the diagram.

Measurements

Measurement record: pipeline ObjID 169, matched to this dialface by inventory number.

Quality grade	B (completeness 99 %)
Dial surface	cone (decisive) · fit residual mm: cone 0.70, cylinder 3.67, sphere 3.76
Latitude φ	35.19 ± 3.40° (consensus of witnesses)
Klima	Rhodes (IV), Delos, Athens
Engraved lines	10 hour lines, 3 day lines
Cone half-angle α	38.3 ± 0.13° (cone residual on all points 0.72 mm)
Measured	2026-06-12 20:28

What the dial shows at this latitude

	Winter solstice	Equinox	Summer solstice
Noon altitude of the Sun	31.1°	54.8°	78.5°
Noon shadow (gnomon heights)	1.66	0.70	0.20
Length of the day	9.6 h	12.0 h	14.4 h
Length of a seasonal hour	48 min	60 min	72 min

Computed for the measured latitude with the obliquity of the JPL ephemeris at 101 BC (year -100). The latitude is the one the dial was made for, not a find-spot coordinate.

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References

– Gibbs, Sharon L., Greek and Roman Sundials, New Haven and London, 1976, p. 289, p. 292, plate 45.
– Severino, Nicola, De Monumentis Gnomonicis apud graecos et romanos. Le meridiane greco-romane. La storia, il catalogo, gli articoli, Roccasecca, 2003, p. 19.
– Moore, R., Kazantzakis, N., Reflections on Greece, New York, 1971, (photograph, wrongly located in Olympia).
– Bonnin, Jérôme, La Mesure du temps dans l'Antiquité, Paris, 2015, A 103.
– Winter, Eva, Zeitzeichen. Zur Entwicklung und Verwendung antiker Zeitmesser, Berlin and Boston, 2013, p. 499.