I love ancient stories about omens. Here's one:

contractis ad Bononiam triumvirorum copiis aquila tentorio eius supersedens duos corvos hinc et inde infestantis afflixit et ad terram dedit, notante omni exercitu futuram quandoque inter collegas discordiam talem qualis secuta est, atque exitum praesagiente.
When the troops of the [second] Triumviri were collected about Bolognia, an eagle, which sat upon [Augustus'] tent, and was attacked by two crows, beat them both, and struck them to the ground, in the view of the whole army; who thence inferred that discord would arise between the three colleagues, which would be attended with the like event: and it accordingly happened.
Sueton, The Lives of the Ceasars: Augustus, 96.1