Agger prope molem est.

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

So:

• prope = near
• molem = accusative singular of moles

That is why Latin says prope molem, not prope moles.

A very literal breakdown is:

• agger = embankment / rampart
• prope molem = near the mass / barrier / structure
• est = is

Agger is nominative singular because it is the subject of est.

In other words, agger is the thing that is somewhere.

So in this sentence:

• agger = the subject
• est = the verb
• prope molem = a phrase telling where the subject is

This is the same basic idea as in English The embankment is near the structure.

This is a matter of third-declension noun forms.

The dictionary form is moles. Its accusative singular is molem.

A learner often has to get used to the fact that third-declension nouns can change quite a bit in form:

• nominative singular: moles
• accusative singular: molem

So if you see molem, you should think: this is likely an accusative singular form of moles.

Because Latin word order is much more flexible than English word order.

English normally requires something like:

• The embankment is near the structure.

Latin can place the verb in different positions, and it is very common for the verb to come last. So:

• Agger prope molem est.

is a perfectly normal Latin arrangement.

The meaning does not change just because est comes at the end. The ending of the words tells you their roles more than the position does.

No. Classical Latin does not have articles like English the and a/an.

So agger can mean:

• an embankment
• the embankment

and molem can mean:

• a mass / barrier / structure
• the mass / barrier / structure

You decide from the context which English article sounds best.

No. Prope can be used in more than one way.

Here it is a preposition meaning near, followed by the accusative:

• prope molem = near the structure

But prope can also be an adverb in some contexts, meaning something like near or nearly.

In this sentence, though, it is clearly a preposition because it is followed by molem.

Sometimes ad can mean something like at or near, but prope is a more direct and straightforward way to say near.

So:

• prope molem est = is near the structure

Using prope makes the spatial relationship very clear.

A learner should usually understand:

• prope = near
• ad = to, toward, at, near (depending on context)

In this sentence, prope is the simplest and best match for English near.

Agger usually means something like:

• embankment
• mound
• rampart
• earthwork

In military or engineering contexts, it often refers to a raised bank of earth or a constructed mound.

So the sentence suggests a physical structure located near another large structure or mass.

Moles is a word with a somewhat broad range of meanings. Depending on context, it can mean:

• mass
• bulk
• barrier
• large structure
• pier / mole in some settings

So prope molem could mean near the mass, near the barrier, or near the large structure, depending on the context already given.

This is normal in Latin: one word can have several related meanings, and context tells you which one fits best.

Yes. It is a completely normal and complete Latin sentence.

It has everything it needs:

• agger = subject
• est = verb
• prope molem = phrase describing location

Latin often expresses ideas very compactly. Short sentences like this are common, especially in beginner material, descriptions, and narrative passages.