Mense Martio ver incipere videtur, et Martius agricolas ad campos revocat.

Because Latin is using the ablative of time when: mense Martio means in the month of March.

• mense = in the month
• Martio = of March / March-like, agreeing with mense

A nominative phrase like mensis Martius would mean the month of March as the subject of a sentence, not in March.

Martio is ablative singular because it agrees with mense, which is also ablative singular.

Latin adjectives must match the nouns they describe in:

• gender
• number
• case

So:

• mense = ablative singular masculine
• Martio = ablative singular masculine

Together they form mense Martio = in the month of March.

Because the word is doing two different jobs.

1. In mense Martio, Martio is an adjective agreeing with mense:

   • in the month of March

2. In et Martius agricolas ad campos revocat, Martius is nominative singular and acts as the subject:

   • March calls the farmers back to the fields

So the different endings show different grammatical roles.

It is effectively doing both kinds of work in the sentence.

• In mense Martio, it is clearly an adjective modifying mense.
• In the second clause, Martius is used almost like a noun, meaning March.

This is very natural in Latin. A word that is originally adjectival can be used by itself when the meaning is clear.

Because ver is the subject of incipere.

In ver incipere videtur, the thing that seems to begin is spring, so ver must be in the nominative.

Even though English often says it seems that spring is beginning, Latin prefers a structure more like:

• spring seems to begin

So ver stays the subject.

Because Latin commonly uses videor / videtur with an infinitive to mean seem to ...

So:

• ver incipere videtur = spring seems to begin

Literally, it is:

• spring is seen/seems to begin

This is a very common Latin pattern. Instead of using a full subordinate clause like English often does, Latin often uses:

• subject + infinitive + videtur

Examples of the same pattern:

• puer dormire videtur = the boy seems to be sleeping
• urbs cadere videtur = the city seems to be falling

Because videtur is the form that means seems here.

• videt = he/she/it sees
• videtur = he/she/it is seen and, very commonly, he/she/it seems

So in this sentence:

• ver incipere videtur = spring seems to begin

This is one of the standard meanings of the passive form of video.

Both are present tense:

• videtur = seems
• revocat = calls back

The present tense is used because the sentence expresses a general truth or customary seasonal pattern, not one single historical event.

So the sense is something like:

• In March, spring seems to begin, and March calls the farmers back to the fields.

It is a regular, recurring fact.

Because agricolas is the direct object of revocat.

• Martius = subject
• revocat = verb
• agricolas = the people being called back

So:

• Martius agricolas revocat = March calls the farmers back

Since agricola is a first-declension masculine noun, its accusative plural is agricolas.

Because ad shows movement toward a place.

• ad campos = to the fields
• in campis = in the fields

Since the idea is that March is calling the farmers back to the fields, Latin uses ad plus the accusative.

So:

• revocat ad campos = calls back to the fields

The prefix re- often adds the idea of back or again.

So:

• vocat = calls
• revocat = calls back

That fits the seasonal idea: the farmers are returning to field work after winter.

Because Latin often uses the plural when speaking generally about fields, farmland, or the open countryside.

So ad campos does not necessarily mean a specific set of several fields in a mathematical sense. It can simply mean:

• to the fields
• out to farm work
• back to the countryside

This sounds natural in both Latin and English.

Yes, but it is also very normal Latin word order.

Sentence: Mense Martio ver incipere videtur, et Martius agricolas ad campos revocat.

A few things to notice:

• Mense Martio comes first to set the time: In March
• ver is placed before incipere videtur, making the subject clear
• Martius begins the second clause for emphasis: March is what brings the change
• revocat comes at the end of its clause, which is very common in Latin

Latin word order is more flexible than English, so the endings carry much of the grammar.

Because Latin does not need a dummy subject like English it.

English says:

• It seems that spring is beginning

But Latin more naturally says:

• Spring seems to begin
• ver incipere videtur

So Latin makes the real idea, ver, the grammatical subject instead of inserting an empty it.

It has two main clauses joined by et:

1. Mense Martio ver incipere videtur

   • In March, spring seems to begin

2. et Martius agricolas ad campos revocat

   • and March calls the farmers back to the fields

So the overall pattern is:

• time expression
• first main clause
• et
• second main clause

This is a straightforward and elegant Latin sentence.