1. Gallia est omnis divisa in partes tres, quarum unam incolunt Belgae, aliam Aquitani, tertiam qui ipsorum lingua Celtae, nostra Galli appellantur. Hi omnes lingua, institutis, legibus inter se differunt. Gallos ab Aquitanis Garumna flumen, a Belgis Matrona et Sequana dividit.

2. Word Order Gallia est omnis divisa in partīs trīs
Why
Gallia est omnis divisa in partīs trīs
instead of:
Omnis Gallia in tres partes divisa est
first word sets topic
postponing omnis makes it emphatic
dividing divisa est suggest predicative adjective rather than perfect passive
Caesar regularly puts cardinal numbers after the noun
putting tris after partis leads naturally into subsequent partitives

3. Ellipsis
Ellipsis is the intentional omission of words understood in context.
three friends entered the house, but only two left.
the principal praised her, but not him.
most of the dogs came to the door, but one stayed behind.

4. Asyndeton The purposeful omission of conjunctions
we work hard, we play hard
Mr. Switzer praised the students, faculty, staff.
We dislike all vegetables – especially broccoli, corn, turnips, sprouts.
asyndeton speeds up the reading of a line, and brings an emphatic effect to the words

5. Horum omnium fortissimi sunt Belgae, propterea quod a cultu atque humanitate provinciae longissime absunt, minimeque ad eos mercatores saepe commeant atque ea {quae ad effeminandos animos pertinent} important, proximique sunt Germanis, {qui trans Rhenum incolunt}, {quibuscum continenter bellum gerunt.}

6. Qua de causa Helvetii quoque reliquos Gallos virtute praecedunt, quod fere cotidianis proeliis cum Germanis contendunt, cum aut suis finibus eos prohibent aut ipsi in eorum finibus bellum gerunt.

7. Eorum una, pars, {quam Gallos obtinere dictum est,} initium capit a flumine Rhodano, continetur Garumna flumine, Oceano, finibus Belgarum, attingit etiam ab Sequanis et Helvetiis flumen Rhenum, vergit ad septentriones.

8. Belgae ab extremis Galliae finibus oriuntur, pertinent ad inferiorem partem fluminis Rheni, spectant in septentrionem et orientem solem. Aquitania a Garumna flumine ad Pyrenaeos montes et eam partem Oceani {quae est ad Hispaniam} pertinet; spectat inter occasum solis et septentriones.

9. atque / ac neque / nec generally a more emphatic conjunction than et:
“and also, and indeed, and so”
atque used before a vowel or h, ac before a consonant
neque / nec
used indifferently before vowels and consonants
in nec the negation is more prominent, while in neque the connective force is more prominent
when used alone = “and not” [Roman authors never wrote et non]
when with another negative = “nor”
in pairs = “neither / nor”

11. Septentrones = ‘north’ septem + triones ‘seven + oxen’
Ursa Minor
Ursa Major
“Plough”
← Polaris
“North Star”
this etymology given by Varro

12. Bootes “Ox-driver” Plough
Arcturus (“Bear-Guardian”) is 3rd brightest star, after Sirius and Canopus
Plough