The corpus, every claim citable.

Varāhamihira's Pañcasiddhāntikā (505 CE) summarizes and ranks five astronomical schools; the Romaka ("Roman") Siddhānta places in the top three. Its luni-solar yuga of 2,850 years with 1,050 intercalary months is exactly 150 Metonic cycles (19 years, 7 intercalations each), and its epoch is reckoned from sunset at Yavanapura — Alexandria. Greco-Roman astronomy circulated inside the Indian canon, openly named and rated.

The Panchasiddhantika: The Astronomical Work of Varaha Mihira · tr. G. Thibaut & Sudhakara Dvivedi, 1889

Pañcasiddhāntikā XII (505 CE) preserves the Paitāmaha Siddhānta: a five-year luni-solar calendar of 1,830 civil days, intercalating every 30 months, with its epoch at the asterism Dhaniṣṭhā — the winter-solstice marker of the Vedāṅga Jyotiṣa tradition, datable by precession to c. 1400–1200 BCE. Varāhamihira transmits the system faithfully while ranking it "far from the truth" — the Indian canon documenting and superseding its own oldest astronomy.

The Panchasiddhantika: The Astronomical Work of Varaha Mihira · tr. G. Thibaut & Sudhakara Dvivedi, 1889