Retro villam hortus parvus est.

Because retro takes the accusative when it means behind.

So:

• retro = behind
• villam = the house / a house in the accusative singular

A native English speaker may expect a location word to work differently, because English just says behind the house without showing case on house. In Latin, however, many prepositions require a specific case, and here that case is the accusative.

Because hortus is the subject of the sentence.

The sentence is basically:

• Retro villam = behind the house
• hortus parvus est = a small garden is

So the thing that is there is the garden, and subjects are put in the nominative.

This can feel strange to English speakers because English often says There is a small garden behind the house, where garden comes after the verb. But in Latin, hortus is still the subject, so it stays nominative.

Because parvus describes hortus, and Latin adjectives must agree with the nouns they describe.

So hortus is:

• masculine
• singular
• nominative

Therefore parvus must also be:

• masculine
• singular
• nominative

That is why you get hortus parvus, not some other form.

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

In English, we normally say small garden, with the adjective first. In Latin, both orders are possible:

• parvus hortus
• hortus parvus

Both can mean small garden. In a simple sentence like this, putting the adjective after the noun is perfectly normal.

Because Latin often puts the verb near or at the end of the sentence.

English usually prefers something like:

• A small garden is behind the house

Latin often prefers:

• Behind the house a small garden is

This does not change the meaning. It is just a common Latin sentence pattern.

Because Latin has no articles.

So Latin does not have separate words that exactly equal English a, an, or the.

That means:

• villa can mean a house or the house
• hortus parvus can mean a small garden or the small garden

The context tells you which is most natural in translation.

Here it is functioning like a preposition, because it introduces a noun phrase: retro villam.

So in this sentence, it works as:

• retro = behind
• villam = its object

A learner may know retro from English words like retroactive or retro style, but in Latin it can be an actual word meaning back / behind.

Yes.

Both are good English translations of the same Latin sentence.

Latin does not need a special word for there is here. It simply says:

• hortus parvus est = a small garden is

In natural English, we often turn that into:

• There is a small garden behind the house

So the two English versions express the same basic idea.

We know because of the endings.

• hortus is masculine singular nominative
• parvus is also masculine singular nominative

That matching pattern shows that parvus describes hortus.

Meanwhile, villam is accusative, so it belongs with retro, not with hortus.

Latin endings often tell you which words belong together more clearly than word order does.

Often, yes.

For example, these would still express essentially the same idea:

• Hortus parvus retro villam est
• Parvus hortus retro villam est
• Retro villam parvus hortus est

The exact emphasis may shift a little, but the core meaning stays the same because the endings show the grammar.

That said, some word orders sound more natural than others, and beginner textbooks often use a straightforward pattern like the one in your sentence.