Militibus laborantibus, faber turrim novam munit et portam firmiorem facit.

The main subject is faber = the craftsman / smith / builder.

You can tell because faber is in the nominative singular, and the main verbs munit and facit are both third-person singular. So the craftsman is the one doing the main actions.

Militibus laborantibus is ablative plural, and it is an ablative absolute.

That means:

• militibus = soldiers in the ablative plural
• laborantibus = working in the ablative plural, agreeing with militibus

An ablative absolute is a kind of side phrase that gives the circumstances of the main action. It often translates as:

• while the soldiers are working
• when the soldiers are working
• with the soldiers working

So this phrase sets the scene for the main clause.

Because it has to agree with militibus.

Since militibus is ablative plural, the participle must also be ablative plural: laborantibus.

If it were laborantes, that would be nominative or accusative plural, which would not fit this construction.

So the matching forms show that militibus laborantibus belongs together as one phrase.

Laborantibus is the present active participle of laborare.

Its basic meaning is working or toiling.

Because it is a present participle, it usually shows action happening at the same time as the main verb. So the idea is:

• the soldiers are working
• at the same time that
• the craftsman fortifies the tower and strengthens the gate

In form, yes: militibus and laborantibus can be dative plural or ablative plural.

But here it is understood as ablative absolute, not dative, because:

• the phrase stands a little apart from the main clause
• it contains a noun + participle together
• nothing in the main clause is asking for a dative

So context makes ablative the natural reading.

Because their subject is faber, which is singular.

• munit = he/she fortifies
• facit = he/she makes

Since faber is one person, the verbs are singular too.

Because it is the direct object of munit.

The craftsman is doing something to the tower, so tower must be in the accusative:

• turrim = tower (accusative singular)
• novam = new (accusative singular feminine, agreeing with turrim)

So turrim novam munit means he fortifies a new tower or he fortifies the new tower, depending on context.

Firmiorem is the comparative form of firmus, meaning stronger.

It agrees with portam:

• portam = gate (accusative singular feminine)
• firmiorem = stronger (accusative singular feminine)

In portam firmiorem facit, Latin uses facere plus an object plus a describing word:

• facit = makes
• portam = the gate
• firmiorem = stronger

So the whole phrase means he makes the gate stronger.

Latin often leaves that unstated when the comparison is obvious from context.

So firmiorem can mean:

• stronger than before
• stronger than it was
• more solid

The sentence does not need to say exactly what the gate is being compared with.

They are related but not identical.

• munit means fortifies, defends, or builds up as a fortification
• facit means makes

So:

• turrim novam munit = he fortifies the new tower
• portam firmiorem facit = he makes the gate stronger

The first verb is more specific and military/defensive. The second is more general.

Latin word order is much more flexible than English word order because the endings show each word’s job in the sentence.

This sentence begins with militibus laborantibus to give the background first: while the soldiers are working...

Then comes the main subject faber, followed by the objects and verbs.

A Latin reader understands the structure mainly from the case endings and verb endings, not just from position.

Because Latin has no articles.

So faber can mean:

• the craftsman
• a craftsman

and turrim novam can mean:

• the new tower
• a new tower

The translator chooses the or a from context.

Yes. That is very common.

Militibus laborantibus could be translated as:

• while the soldiers are working
• when the soldiers are working
• with the soldiers working
• sometimes even as the soldiers work

All of these try to capture the same basic idea: the soldiers’ work is the background circumstance for the main action.