Imperator dicit libertatem civium cum salute urbis servandam esse.

The main verb is dicit = says.

So the sentence is built in two parts:

• Imperator dicit = The commander/general says
• libertatem civium cum salute urbis servandam esse = the thing that he says

This second part is an indirect statement.

Because Latin commonly uses the accusative + infinitive construction after verbs of saying, thinking, knowing, hearing, and so on.

Here, after dicit, the idea being reported is put into indirect statement:

• direct form: Libertas civium cum salute urbis servanda est
• indirect form: Imperator dicit libertatem civium cum salute urbis servandam esse

So libertas becomes libertatem, because the subject of the infinitive in an indirect statement goes into the accusative.

Servandam esse is a gerundive of obligation with esse.

It means:

• to be preserved
• more specifically, must be preserved or is to be preserved

So this is not just a plain passive infinitive. It expresses necessity or obligation.

From servo, servare = to preserve, protect, keep safe, Latin forms:

• servanda est = must be preserved
• in indirect statement: servandam esse = to have to be preserved / must be preserved

Because of agreement.

Servandam is:

• feminine
• singular
• accusative

Libertatem is also:

• feminine
• singular
• accusative

But salute is ablative, not accusative.

So servandam must agree with libertatem, not with salute.

That tells you that the freedom is the thing that must be preserved, while cum salute urbis is just an added phrase meaning together with the safety of the city.

Because cum is a preposition here, and when cum means with, it takes the ablative.

So:

• cum salute = with safety
• more naturally here: together with the safety

This is a very common Latin pattern:

• cum amico = with a friend
• cum cura = with care
• cum salute urbis = with the safety of the city

Yes. Here cum is a preposition, not a conjunction.

A native English speaker often sees cum and wonders whether it means when. It can, but not here.

You can tell it is the preposition with because it is followed by a noun in the ablative: salute.

So here:

• cum salute urbis = with the safety of the city
• not when the safety of the city...

Both are genitives.

• civium = genitive plural of cives = of the citizens
• urbis = genitive singular of urbs = of the city

They show possession or close relationship:

• libertas civium = the freedom of the citizens
• salus urbis = the safety of the city

So the structure is:

• libertatem civium = the freedom of the citizens
• cum salute urbis = with the safety of the city

A helpful way to divide it is:

• Imperator — subject
• dicit — main verb
• libertatem civium cum salute urbis servandam esse — indirect statement

Inside that indirect statement:

• libertatem — accusative subject of the infinitive
• civium — genitive depending on libertatem
• cum salute urbis — prepositional phrase
• servandam esse — infinitive phrase expressing necessity

So, very literally, the structure is something like:

The commander says [the freedom of the citizens, together with the safety of the city, to-be-preserved].

That sounds awkward in English, but it is normal Latin syntax.

The sentence does not state the agent.

The gerundive of obligation often tells you that something must be done, without naming who must do it.

So servandam esse means must be preserved, but Latin leaves open the question of by whom.

If Latin wanted to name the responsible person, it could use a dative of agent. But here the speaker simply states the necessity, not the person responsible.

Esse is there because the indirect statement uses an infinitive, and the passive periphrastic in indirect statement needs esse:

• direct: servanda est
• indirect: servandam esse

As for position, Latin word order is flexible, but verbs—especially infinitives—often come toward the end of the clause.

So servandam esse at the end is very natural Latin style. The meaning would stay basically the same if the words were arranged differently, but this order is standard and elegant.