The earliest work on astrology that is extensive, comprehensible, and mostly intact, the Astronomica describes celestial phenomena, and, in particular, the zodiac and astrology. The poem—which seems to have been inspired by Lucretius's Epicurean poem De rerum natura—espouses a Stoic, deterministic understanding of a universe overseen by a god and governed by reason. The fifth book contains a lacuna, which has led to debate about the original size of the poem; some scholars have argued that whole books have been lost over the years, whereas others believe only a small section of the work is missing.