purposes like the calculation of horoscopes. Theo ̄n’s LC directly fulfils this demand, provid-
ing detailed guidance through the HT with no theoretical explanation but illustrated by fully
calculated examples. At the same time, Theo ̄n repeatedly complains about his students’
insufficient skills in geometry and calculation and therefore urges them to turn themselves
to theoretical studies, especially geometrical proofs underlying Ptolemy’s calculations and
tables. One of Theo ̄n’s purposes was thus to turn the Almagest into either an initiation to,
or a consolidation of, his students’ geometrical knowledge (best seen from his commen-
tary on Alm. 1, cf. IA 319.2–3 Rome). He therefore emphasizes its mathematical interest
and its contribution to liberal education (IA 321.10–13 Rome). Theo ̄n saw this interpret-
ative stance as the continuation of Ptolemy’s own work as a commentator of the
ancients, and urged the most able of his companions to go the same way (IA 319.6– 10
Rome). It seems that Theo ̄n shared with them a real veneration for Ptolemy, as an
epigram preserved under his name reveals (Dzielska, 75). In spite of this, Theo ̄n’s project
was essentially different from Ptolemy’s, since Theo ̄n showed no interest in checking or
improving Ptolemy’s models or calculations through new astronomical observations. Even
the extant part of GC, in which such reflections could have been found, shows no effort
in this direction.
Theo ̄n’s IA might betray some influence from P’ own commentary on the Alma-
gest. But, although the Souda notice erroneously makes them contemporaries under Theo-
dosius I, nothing precise is known about their exact dependence – in particular Theo ̄n
never mentions Pappos. Theo ̄n may have derived his interest in classical geometry and
liberal education from him, but he does not seem to have shared Pappos’ special interest
in mathematical heuristics and He ̄ro ̄nian mechanics (H A); he was
apparently more inclined toward accurate descriptions of computational procedures.
Theo ̄n’s ambiguous statement about the study of philosophy in IA (319.20–22 Rome)
shows either his lack of interest or his contempt for such studies, perhaps out of fidelity
to Ptolemy’s preference for mathematical studies over philosophical debates (Alm. 6.15– 19
Heiberg). The scarce testimonies given by the Souda (A-205) and John Malalas’ Chrono-
graphia, may point toward his (plausible) interest in astrological Hermetism (Dzielska, 74–
77). Besides Hupatia, who seems to have proofread IA 3, Theo ̄n mentions other collabor-
ators: one Epiphanios to whom he dedicates LC, IA and GC 4 (most probably one of his
able akroatai) and two “companions” O ̄rigene ̄s and Eulalios, to whom GC 1 – 3 is
dedicated.
In one passage of IA (492.6–8) Theo ̄n mentions an additional case to Elements 6.33 pub-
lished in his own edition of E’s Elements. Heiberg, by comparing the Greek manu-
scripts of the Elements, thought he could determine the precise style and extent of Theo ̄n’s
revisions on Euclid. But more recent research shows the comparison unreliable, partly due to
Heiberg’s neglect of the Arabic and Latin translations of Euclid as well as the complexity of
the direct transmission itself (Vitrac, 27–30). Theo ̄n’s intervention was apparently a stand-
ardization, perhaps motivated by the need to provide better support for geometrical studies.
Heiberg’s attribution of a revision of Euclid’s Optics to Theo ̄n has been shown to rely on
negligible evidence, although it is consistent with Theo ̄n’s quotation of Euclid’s Optics in IA
as well as with his putative knowledge of Pappos’ commentary. But it is not explicitly
attested and is thus nothing more than a plausible guess. Similarly, much doubt has been
cast on Heiberg’s attribution to Theo ̄n of revised editions of Euclid’s Catoptrics and HT.
Neugebauer (Isis 40, 1949) conjectured that the contents of Theo ̄n’s treatise on the “small
astrolabe” correspond to Yaqubi’s summary of Ptolemy’s treatise on the plane astrolabe
THEO ̄N OF ALEXANDRIA (ASTR.)