The flag is a complicated coat of arms (with three inner scrolls, what's exotic if not incorrect) in a blue background (that's used less than in USA, what doesn't make it less uncreative). Explaining the symbolism is a complex mission, so I'll analyze each quarter separately:
- The two arms, the first holding flowers and the second holding fruits, represent the fertility of the region. The scroll says "vereat aeternum - tutius latente", what means, in Latin, "eternal spring", again a reference to fertility, and "safer hidden", because the the city had hard access for land, being on the other side of Amazon River and Tocantins River.
- The sun represents the beautiful aurora that appeared on the moment the town was founded, the position very near to equator and the warm climate of the "tawny city". The scroll says "rectior cum retrogradus" i.e. "straighter looking backwards". The aforementioned aurora is saw on background.
- The castle is a reference to the founder of the city, Francisco Caldeira Castelo Branco, whose surname, in Portuguese, means "white castle". It's adorned with the Portuguese inescutcheon.
- A cow and an ass looking astonished to the sky (from the nativity scene) represent the namesake city of Bethlehem, in Judea. The scroll says "nequaquam minima est" i.e. "noway is minor".
The white tower represents both Castelo Branco (the founder) and the Forte da Natividade ("Nativity Fort"), the initial mark of the city. It represents Belém, for example, in the coat of arms of the Marine Corps battalion settled on the city. The Portuguese inescutcheon was simplified to one of its elements: a single quina. The wavy blue fields represent the rivers, used as symbols of fertility and regional landmark, while the lilac field represent the aurora that appeared.
I think I could find at least one better arrangement:
Now the flag is resumed to the blue field, the white tower and the golden sun, that represents an amalgamation of symbolisms: the aurora, the equator, the climate, the fertility, the "tawny city".
This flag would be much better, in my opinion, if it was square, although Brazilian typical 7:10 ratio is sufficiently large.
Feel free to comment, your opinion is welcome.
I might post here again tomorrow, only if everything goes alright.