Ocean

In Cicero's prosecution of Verres, the corrupt former governor of Sicily, he imagines that Verres' lawyers will try to argue that he should be spared because of his great service to the Republic in keeping Sicily free from rebel slaves. It's a tactic that worked in the case of Manius Aquilius, but to Cicero the idea of Verres as a heroic general is laughable and he thoroughly demolishes any claim he may have to be so (perhaps a little disingenuously). Part of his argument is that the rebel slaves (led by Spartacus) running around Italy at the time didn't have boats (something which Marcus Crassus had taken care to ensure), and so there was no danger at all of war crossing from Italy to Sicily.

Quid dicis? an bello fugitivorum Siciliam virtute tua liberatam? ... "At cum esset in Italia bellum tam prope a Sicilia, tamen in Sicilia non fuit." Quid mirum? ... Aditus omnis hominibus sine ulla facultate navium non modo disiunctus sed etiam clausus est, ut illis quibus Siciliam propinquam fuisse dicis facilius fuerit ad Oceanum pervenire quam ad Peloridem accedere.

What are you saying? Perhaps that Sicily was kept safe by your courage? "Even though there was war in Italy, so short a distance from Sicily, yet it did not cross in Sicily." What's so amazing about that? Every approach to Sicily is not only cut off, but even completely closed to those without access to boats, so that it would have been easier for those whom you say were close to Sicily, to reach Ocean than to approach Pelorus.

What Cicero means by Oceanum in the last line is not what we would understand these days. For the Romans, Ocean was a river that encircled the world. So Cicero doesn't just mean that it would be easier for the rebel slaves to get to a large body of water, than to get to Sicily, but that it would be easier for them to walk all the way up Italy, across the alps, through the frozen, uncivilized lands that lay to the north and arrive eventually at the bank of this river, than to cross the two kilometres or so of water that divide Italy and Sicily.
 
To give you an idea of how Cicero may have imagined these distances, you can see the river Ocean running around the top of the fascinating map at the top of this post (from Pomponius Mela, a first century geographer). It takes a bit of imagination, but you should also be able to find Sicily, and to see by contrast the tiny distance from Pelorus to the Italian mainland (Pelorus is at the north-eastern tip of Sicily).