Miles portam custodit, et cives eum laudant.

Because miles is a singular nominative form of a third-declension noun.

A native English speaker may expect -s to mark a plural, but in Latin that is not how it works. In this word, the -es is simply part of the normal singular form:

• miles = soldier (subject, singular)
• milites = soldiers (subject, plural)

So here miles is one soldier, not several.

Because portam is the accusative singular form, used for the direct object.

The soldier is doing the action of guarding, and the gate is what he is guarding. That makes gate the direct object, so Latin uses the accusative:

• porta = gate as a subject
• portam = gate as a direct object

So in this sentence:

• miles = subject
• portam = direct object

Custodit is the third-person singular present active indicative of custodire, meaning to guard or to watch.

It matches the subject miles, which is singular:

• ego custodio = I guard
• tu custodis = you guard
• ille/illa custodit = he/she guards

So miles portam custodit means the soldier guards the gate.

Here cives means citizens and is the nominative plural subject of laudant.

You can tell it is plural because the verb is also plural:

• laudat = he/she praises
• laudant = they praise

So cives laudant means the citizens praise.

A learner might notice that cives could also be accusative plural in some contexts, but here the verb ending shows that cives is the subject.

Eum means him and refers back to miles.

Latin often uses a pronoun instead of repeating a noun that has just been mentioned. So instead of saying:

• et cives militem laudant

the sentence says:

• et cives eum laudant

Both are possible. Eum is simply smoother and more natural here.

Because of gender.

• miles is masculine
• porta is feminine
• eum is masculine accusative singular, meaning him
• If it referred to porta, we would expect eam, meaning her/it

So eum must refer back to miles, not portam.

Because the subject of the second clause is cives, which is plural.

Latin verbs agree with their subjects in number:

• laudat = he/she praises
• laudant = they praise

Since cives means citizens, the plural verb laudant is required.

Latin usually has no articles, so it does not have separate words for the or a/an.

That means a noun like miles can mean:

• the soldier
• a soldier

The exact English choice depends on context. The same is true for portam and cives.

Not as much as it is in English.

Latin word order is more flexible because the endings show what each word is doing:

• miles = subject
• portam = object
• custodit = verb
• cives = subject
• eum = object
• laudant = verb

So Latin could rearrange the words in various ways without changing the basic meaning, for example:

• Portam miles custodit
• Cives eum laudant
• Eum cives laudant

However, the original order is a very normal and clear one.

There are two main cases here:

• Nominative for subjects
• Accusative for direct objects

So the sentence breaks down like this:

• miles — nominative singular, subject
• portam — accusative singular, direct object
• cives — nominative plural, subject
• eum — accusative singular, direct object

This is a very common Latin pattern: subject + object + verb.

Et simply means and.

It joins the two clauses:

• Miles portam custodit
• cives eum laudant

So the full sentence has two connected ideas:

• the soldier guards the gate
• the citizens praise him

Latin often uses et exactly the way English uses and.

Not easily in this sentence, because eum is the object of laudant and tells us whom the citizens praise.

Latin often omits subject pronouns, because the verb ending already shows the subject. But object pronouns are different: if you remove eum, then cives laudant would just mean the citizens praise, without saying whom they praise.

So eum is needed unless the noun is repeated instead, as in cives militem laudant.

Because the verb ending already includes that information.

In custodit, the -t tells you the subject is third person singular:

• custodio = I guard
• custodis = you guard
• custodit = he/she/it guards

So Latin usually does not need to add a separate subject pronoun unless it wants special emphasis. Here miles is already the subject, so no extra word for he is needed.