Ancient Sundials

Dialface ID 25

ObjID25-1

Holder:: Soprintendenza Speciale per i Beni Archeologici di Napoli e Pompei, Pompei, Italy
Site:: Pompei, Italy
Material:: Marble, White with streaks of gray
Dating:: before 79 CE
Type:: Sphere, Spherical-cut dials--central gnomon point
Inventory Number:: 34218
Site Geolocation:: Lat.: 40.7503, Long.: 14.4871

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Abstract

The sundial has plain sides. A torus moulding connects the oblique upper and lower front parts. Gibbs: The base of a bronze gnomon remains in a lead filled gnomon hole in the top surface of the dial. Traces of red orange color remain in the eleven hour lines and three day curves. [...] Bronze and lead remain in the mount hole in the bottom surface. Severino: Sul "top" dell'orologio si vede bene la base rimanente dello gnomone che in questo caso non è conservato. Il tracciato orario conserva solo 10 linee orarie e le curve dei solstizi ed equinozi ed è fatto con buona cura. Nessun colore si evince sulla superficie e nessun rilievo o iscrizione.

Measurements

Measurement record: pipeline ObjID 25, matched to this dialface by inventory number.

Quality grade	B (completeness 97 %)
Dial surface	sphere (decisive) · fit residual mm: cone 5.14, cylinder 5.85, sphere 2.08
Latitude φ	39.46 ± 4.01° (consensus of witnesses)
Klima	Athens, Hellespont (V), Delos
Engraved lines	10 hour lines, 3 day lines
Cone half-angle α	not shown: surface fit decisively sphere: cone-specific quantities do not apply
Measured	2026-06-12 20:37

What the dial shows at this latitude

	Winter solstice	Equinox	Summer solstice
Noon altitude of the Sun	26.8°	50.5°	74.3°
Noon shadow (gnomon heights)	1.98	0.82	0.28
Length of the day	9.2 h	12.0 h	14.8 h
Length of a seasonal hour	46 min	60 min	74 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. 140.
– Severino, Nicola, De Monumentis Gnomonicis apud graecos et romanos. Le meridiane greco-romane. La storia, il catalogo, gli articoli, Roccasecca, 2003, p. 24.
– Moore, R., Kazantzakis, N., Reflections on Greece, New York, 1971, wrong localization Olympia.