Dictionary of Greek and Roman Biography and Mythology/Theodosius (literary) 1.

THEODO′SIUS, literary. 1. Of Bithynia. a mathematician, who is referred to by Vitruvius (ix. 9. s. 8. § 1, Schneid.) as the inventor of a universal sun-dial (horologium πρὸς πᾶν κλῖμα). Strabo (xii. p. 566) mentions him among the eminent natives of Bithynia, and informs us that his sons were also mathematicians. He must have lived before the time of Augustus, and therefore he cannot be, as some have supposed, the same person as Theodosius of Tripolis, who appears to have flourished later than the reign of Trajan. (See No. 2.)