Prope murum rubus spinas longas habet, itaque pater pueros monet ne eo propius accedant.

Because prope is being used as a preposition here, and as a preposition it takes the accusative.

• prope murum = near the wall

Latin prope can also be an adverb by itself, but in this sentence it has an object, so it is clearly a preposition.

The subject is rubus.

So the first clause breaks down like this:

• rubus = subject
• spinas longas = direct object
• habet = verb

In other words, the bush has long thorns.

Because spinas is the direct object of habet, and longas agrees with spinas in case, number, and gender.

• spinas = accusative plural feminine
• longas = accusative plural feminine

That agreement is exactly what you would expect from a noun and its adjective.

Itaque means and so, therefore, or so.

It connects the two ideas logically:

• the bush has long thorns
• therefore the father warns the boys

So it introduces the consequence of the first clause.

Monere commonly takes the person warned as a direct object.

So here:

• pater = the father = subject
• pueros = the boys = direct object
• monet = warns or advises

Then Latin adds another clause to say what the boys are being warned not to do.

Because after a verb like monet, Latin normally uses ne + subjunctive to mean that ... not.

So:

• monet ne accedant = he warns them not to approach

Non usually negates a simple statement, but ne is the normal negative word in this kind of subordinate clause.

Because it stands in a clause introduced by ne after monet.

This kind of clause regularly takes the subjunctive in Latin. The father is warning the boys not to do something, so Latin expresses that with:

• monet
• ne ... accedant

That is a standard construction.

Because the main verb monet is present tense, so Latin normally uses the present subjunctive here.

• monet ne ... accedant = present main verb + present subjunctive

If the main verb were past, you would usually expect an imperfect subjunctive instead:

• monuit ne ... accederent

This is part of Latin sequence of tenses.

Because the understood subject of accedant is the boys.

Even though pueros is accusative in the main clause as the object of monet, those same boys are the ones who would perform the action of approaching. Latin does not need to repeat the subject if it is already clear.

Together, eo propius means closer to it, closer to that place, or simply any nearer in context.

• propius = nearer, the comparative form related to prope
• eo points back to the thing or place already being discussed

So the father warns them not to go nearer to the dangerous area.

Here it is an adverb.

It describes how they would approach:

• accedant = they approach / come near
• propius = more nearly / nearer

If propius were an adjective here, it would need to agree with a noun. It does not, so it is adverbial.

Because Latin word order is flexible, and it is very common for the verb to come at or near the end of the clause.

So ne eo propius accedant is perfectly natural Latin. It also gives a nice sense of buildup, saving the key action, approach, for the end.

Because accedere already means approach or come near, and Latin does not always need an extra preposition if the direction or reference point is clear from context.

Here eo propius already expresses the idea of moving nearer, so no ad is necessary.