Puer per limitem ad agrum ambulat.

Because puer is the subject of the sentence, so it is in the nominative singular.

In Latin, the subject is usually put in the nominative case. Here, puer means boy and is the one doing the action of ambulat.

Ambulat is:

• 3rd person singular
• present tense
• active voice
• indicative mood

It comes from ambulare, meaning to walk.

So ambulat means he walks or is walking, depending on context.

They are accusative because they are the objects of the prepositions:

• per takes the accusative
• ad also takes the accusative

So:

• per limitem
• ad agrum

Even though both nouns are accusative, they are not direct objects of the verb. They are part of prepositional phrases.

Per is a preposition that usually means something like through, along, or by way of, depending on context.

It shows the route or path involved in the action.

Because per governs the accusative, limes becomes limitem.

Ad is a preposition that usually means to, toward, or up to.

It shows the destination or goal of the movement.

Because ad governs the accusative, ager becomes agrum.

So in this sentence:

• per limitem gives the route
• ad agrum gives the destination

They answer two different kinds of questions:

• per limitem = by what route?
• ad agrum = to where?

This is a very common pattern in Latin movement expressions:

• one phrase can show the path taken
• another can show the endpoint

No. Ambulare is normally intransitive, so it does not need a direct object.

The accusative nouns here might look like objects at first, but they are not direct objects of ambulat. They belong to the prepositions:

• per limitem
• ad agrum

So the structure is not walks something. It is walks through X to Y.

Because both are accusative singular masculine, but they come from different declensions.

• agrum comes from ager, a 2nd-declension noun
• limitem comes from limes, a 3rd-declension noun

So they are not using the same pattern for every form, but in this particular case both happen to end in -m.

Here they are:

• puer: 2nd declension, masculine
• ager → agrum: 2nd declension, masculine
• limes → limitem: 3rd declension, masculine

This is useful because Latin noun endings depend on both case and declension.

Because Latin does not have articles like English.

So a Latin noun such as puer can mean:

• the boy
• a boy

Which one is best depends on context.

English requires an article in most cases, but Latin usually does not.

Yes. Latin word order is more flexible than English word order because the endings show the grammatical roles.

So this sentence could be rearranged in various ways without changing the basic meaning, for example:

• Puer ad agrum per limitem ambulat
• Ad agrum puer per limitem ambulat
• Per limitem puer ad agrum ambulat

The exact order can change the emphasis, but the case endings still show what each word is doing.

Because ad requires the accusative, not the nominative.

The dictionary form is ager, but after ad it must change to agrum.

This is a very common thing in Latin: the form you memorize from the dictionary is often not the form you use in a sentence.

A good first pass is:

1. Find the verb: ambulat
2. Find the subject in the nominative: puer
3. Notice the prepositions:
   • per limitem
   • ad agrum

So the core structure is:

• subject: puer
• verb: ambulat
• prepositional phrases: per limitem, ad agrum

That is a very useful reading strategy for Latin sentences in general.