Lapis terminalis prope agrum arcifinium stat.

Because lapis is in the nominative singular, which is the case normally used for the subject in Latin.

Here, lapis means stone, and it is the thing doing the action of stat. So:

• lapis = subject
• stat = stands / stands situated

That is why lapis is nominative, not accusative or another case.

Terminalis is an adjective modifying lapis.

So lapis terminalis means something like boundary stone or boundary-marker stone.

It agrees with lapis in:

• case: nominative
• number: singular
• gender: masculine

Even though lapis is a noun of the third declension, and terminalis is an adjective, they still agree grammatically.

Because terminalis is a third-declension adjective, not a first/second-declension adjective.

Many Latin adjectives have forms like:

• masculine/feminine nominative singular: -is
• neuter nominative singular: -e

So terminalis is the correct nominative singular masculine form to agree with lapis.

A learner might expect terminalus, but that is not a real form here.

Because prope is being used as a preposition, and when it is a preposition, it takes the accusative case.

So:

• dictionary form: ager = field
• accusative singular: agrum

That is why Latin says prope agrum = near the field.

Not always. Prope can be:

• an adverb: near, nearby
• a preposition with the accusative: near

In this sentence it is a preposition, because it introduces a noun phrase:

• prope agrum arcifinium

So here it means near + object.

Arcifinium modifies agrum.

So the phrase is:

• agrum arcifinium

Just like terminalis agrees with lapis, arcifinium agrees with agrum in:

• case: accusative
• number: singular
• gender: masculine

This tells you that arcifinium belongs with agrum, not with lapis.

Because adjectives agree with the nouns they modify.

Since agrum is accusative singular masculine after prope, the adjective describing it must also be accusative singular masculine:

• agrum = accusative singular masculine
• arcifinium = accusative singular masculine

This is a very common Latin pattern:

• noun + agreeing adjective

Stat is a verb, from stare, meaning to stand.

More specifically, stat is:

• present tense
• third person singular
• active voice
• indicative mood

So it means:

• he/she/it stands
• or, in context, it stands / it is standing
• and sometimes more naturally in English, it stands located or it is situated

Since the subject is lapis, the sense is the stone stands.

Because the subject, lapis, is singular.

In Latin, the verb must agree with its subject in number (and person). Since there is one stone, the verb is singular:

• lapis = singular
• stat = singular

If the subject were plural, the verb would also be plural.

It can mean both, depending on context.

In a sentence like this, stat often suggests not just that the stone is upright, but that it stands in a particular place. English might translate it as:

• stands
• stands near
• is situated near

So the verb can carry a slight sense of position or placement, not only posture.

Because Latin has no articles like English the and a/an.

So a noun like lapis can mean, depending on context:

• a stone
• the stone

And agrum can mean:

• a field
• the field

Latin leaves that distinction to context.

Latin word order is more flexible than English word order, because the endings show the grammatical relationships.

This sentence has a fairly straightforward order:

• Lapis terminalis = subject phrase
• prope agrum arcifinium = prepositional phrase
• stat = verb

But Latin could rearrange these words for emphasis without changing the basic meaning, as long as the forms stay the same.

For example, moving stat earlier or putting prope agrum arcifinium first could change emphasis, but the cases still show who is doing what.

In this sentence, it is best understood as an adjective modifying lapis.

Latin sometimes does use adjectives substantively, but here the most natural reading is:

• lapis terminalis = boundary stone

That is a normal noun + adjective combination.

A learner might want to sort the forms by declension and conjugation:

• lapis — noun, third declension
• terminalis — adjective, third declension
• agrum — from ager, noun, second declension
• arcifinium — adjective of the first/second declension type
• stat — verb from stare, first conjugation

This is useful because the endings come from different patterns, and recognizing those patterns helps you parse the sentence.

By agreement in case, number, and gender.

Here the pairings are:

• lapis terminalis
  • nominative singular masculine
• agrum arcifinium
  • accusative singular masculine

This matching tells you the structure of the sentence.

So even if the word order changed, the endings would still help you connect:

• terminalis with lapis
• arcifinium with agrum