Avia narrat se Syracusis olim in diversorio parvo mansisse.

It has two parts:

• Avia narrat = Grandmother tells / recounts
• se Syracusis olim in diversorio parvo mansisse = that she once stayed in a small inn in Syracuse

So the sentence uses a very common Latin pattern after verbs of saying, thinking, knowing, and the like:

• main verb
• followed by an indirect statement in the accusative + infinitive construction

Here:

• se is the subject of the indirect statement
• mansisse is its verb

So literally, Latin says something like:

• Grandmother tells herself to have stayed...

But in natural English we say:

• Grandmother tells that she stayed...
• or better, Grandmother says that she once stayed...

Se is the reflexive pronoun, and here it refers back to the subject of the main verb, avia.

So:

• Avia narrat se mansisse = Grandmother says that she stayed

The important point is that se refers to the same person as avia.

Compare:

• Avia narrat se mansisse = Grandmother says that she herself stayed
• Avia narrat eam mansisse = Grandmother says that another woman stayed

So a learner often needs to remember:

• se = reflexive, referring back to the subject of the main clause
• eam/eum/eos/eas = non-reflexive, referring to someone else

Because in Latin indirect statement, the subject of the infinitive goes into the accusative.

That is the normal construction:

• dicit puerum venire = he says that the boy is coming
• putat se recte facere = he thinks that he is doing the right thing

So in this sentence:

• se is the subject of mansisse
• but because mansisse is part of an indirect statement, that subject must be accusative

Even though se is logically the one doing the staying, Latin still puts it in the accusative because of the construction.

Because after narrat, Latin normally reports what is said by using an indirect statement.

In English we often use that + a normal verb:

• She says that she stayed

But Latin usually prefers:

• She says herself to have stayed

That is why mansisse is an infinitive.

So:

• narrat = the main verb
• se ... mansisse = the content of what is narrated

This is one of the most important Latin sentence patterns to learn.

Mansisse is the perfect active infinitive of maneo, manere, mansi, mansum.

In indirect statement, the tense of the infinitive shows time relative to the main verb, not necessarily absolute time.

So here:

• narrat = she tells / is telling
• mansisse = the staying happened before the telling

That is why English can translate it as:

• that she stayed
• that she had stayed

Both can be right depending on context.

A useful rule:

• present infinitive = action at the same time as the main verb
• perfect infinitive = action earlier than the main verb
• future infinitive = action later than the main verb

Syracusis is the form used for in Syracuse.

The city name is Syracusae, which is plural in form. With names of cities, Latin often expresses place where without a preposition.

So instead of saying:

• in Syracusis

Latin can simply say:

• Syracusis

This is the special idiom used with towns and small islands.

A grammar book may describe this as:

• a locative use
• or a form identical to the ablative plural in shape

In practice, for a learner, the key idea is simply:

• Syracusis = in/at Syracuse

Because the sentence gives two levels of location:

• Syracusis = the city: in Syracuse
• in diversorio parvo = the specific place inside the city: in a small inn

So the sense is:

• she stayed in Syracuse, in a small inn

This is perfectly natural. English does the same thing:

• She stayed in Syracuse in a small inn

One phrase gives the broader location, and the other gives the more precise one.

Because in with the meaning in / inside / at takes the ablative.

So:

• in diversorio = in an inn
• parvo agrees with diversorio
• therefore both are ablative singular neuter

This is just normal adjective agreement:

• diversorio = ablative singular neuter
• parvo = ablative singular neuter

If in meant motion into, Latin would use the accusative instead:

• in diversorium = into an inn

But here the idea is location, not movement, so the ablative is correct.

Olim is an adverb meaning something like:

• once
• formerly
• long ago
• at one time

In this sentence it tells us when she stayed there.

So:

• se Syracusis olim ... mansisse = that she once / long ago stayed in Syracuse...

It modifies the action of mansisse, not narrat.

Because Latin word order is much freer than English word order. Latin relies more on endings than on position.

Here are some things that may look unusual to an English speaker:

• se comes before a lot of other words
• mansisse is saved for the end
• parvo comes after diversorio

All of that is normal Latin style.

A very common pattern is:

• main clause first
• then the indirect statement
• with the infinitive near the end

And adjectives often come after nouns, though they do not have to.

So even though the order may feel strange in English, the endings make the relationships clear.

Yes. Depending on context, narrat can be translated as:

• tells
• says
• recounts
• relates

So this sentence might be rendered as:

• Grandmother says that she once stayed in a small inn in Syracuse
• Grandmother recounts that she once stayed in a small inn in Syracuse

The core grammar stays the same either way.

Because Classical Latin usually prefers the accusative-and-infinitive construction after verbs of saying and thinking.

English says:

• she says that...

Latin usually says:

• she says someone/something to...

So instead of a that-clause, Latin uses:

• se ... mansisse

This is one of the biggest differences between English and Latin syntax, and this sentence is a very typical example of it.