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4.Visualizing the Invisible The Horologium-Solarium
- University of Wisconsin Press
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Nearly twenty years after construction of the Mausoleum had begun, a new structure was laid out in the northern Campus Martius between the Mausoleum and the Ustrinum: the Horologium-Solarium, a giant sundial that used a red granite obelisk imported from Egypt as its pointer (fig. ; cf. figs. , ). Although the Romans were already well acquainted with the technology and use of small sundials (Gibbs ), no project on this scale had ever before been attempted in Rome. Together with its base, the obelisk stood Roman feet high and cast a shadow that, through the course of the year, traversed the northern surface of the sundial. This dial was a vast pavement of travertine (estimated at ca. × m) inlaid with bronze strips and Greek letters (cf. figs. , ) to mark the sun’s path through the constellations of the zodiac, as well as the solstices, equinoxes, and indications of the seasonal winds. While the general physical appearance of the monument is well known (figs. –), several recent studies have perpetuated misunderstandings about how it actually functioned . Moreover, the monarchical aspects of the project have been almost entirely neglected, though it was at royal institutions like the Great Library at Alexandria that the systematic study of mathematics and astronomy was first organized and put under the patronage of Hellenistic rulers. It seems worthwhile, therefore, to lay out here five developments that contributed to the creation of Augustus’s device in Rome: the growth of the science of mathematical astronomy and accurate timekeeping, the rise of the related field of astrology and Visualizing the Invisible The Horologium-Solarium Heaven divided into fixed parts, The golden sun rules through the twelve constellations —Vergil Georgics .– Figure Figure , Figure a belief in the astral deification of important individuals (catasterism), a growing tendency in literature and art to conceive of time and the cosmos visually, a general Greco-Roman and Etruscan belief in cyclical time, and Rome’s need for an accurate calendar. We can then turn to the specifics of Augustus’s sundial and how it functioned as a monarchic statement of cosmic imperium, and how Octavian commanded the resources necessary to implement this enormous project. Although Greek mathematicians and astronomers were credited with the systematic investigation of the heavens as early as the seventh century (e.g., Berossus the Chaldaean of Kos, ca. , who perhaps taught Thales of Miletos), most advances in astronomy occurred from the fifth century on (Dicks ). Pythagoras of Samos, active in the second half of the sixth century, defined the earth as a sphere in space, surrounded by other heavenly bodies. In addition to observing the morning and evening star and determining the position of the ecliptic (the apparent path of the sun through the constellations) in reference to the earth’s axis, he postulated a philosophical system of numbers, divine harmonies, and a doctrine of the transmigration of the soul that influenced the Neopythagoreans of Augustus’s day. By the first half of the fourth century, Eudoxos of Knidos had conceptualized the circular movements of the sun, moon, and five known planets as a series of spheres that surrounded the earth in a geocentric system. One of his works, the Phainómena, is largely preserved in a later poetic version under the same name by Aratus (see below). With Alexander’s conquest of the Persian empire, and the creation of centers of learning in the capitals of the major Hellenistic kingdoms, further advances became possible under royal authority and patronage. At Alexandria, Aristyllus and Timochares (ca. –) created the first catalogue of star positions, which provided the foundation for later studies of the precession of the equinoxes (discussed in more detail below). Aratus of Soloi in Cilicia (ca. –) spent time at the courts of Antigonos Gonatas of Macedon and Antiochus I of Syria before returning to Macedon, where he died. His surviving work, the Phainómena (Kidd ), was highly influential in Roman circles during the late Republic and early empire; Cicero, Varro, and perhaps Germanicus Caesar all attempted Latin translations (Breysig ; Gain ). Around Aristarchus of Samos argued that the sun, not the earth, was at the center of our universe (Heath ). Although his heliocentric system was generally rejected, he is credited with the invention of two types of sundial: hemispherical (skáphion, a spherical section cut into a rectangular block) and planar (a flat sundial that can be laid horizontally on the ground or set vertically on a wall; cf. fig. ). The Horologium-Solarium [18.219.22.169] Project...
