Can you think of any? The most famous I can think of is: I fear all we have done is to awaken a sleeping giant and fill him with a terrible resolve. It was actually written for the movie Tora! Tora! Tora! which means a number of historians have failed to do their homework.
veni, vidi, vici! (I came, I saw, I conquered)...attributed to Julius Caesar according to couple of different historians who were born some 80-100 years after the fact, with differing versions of how it was delivered...so it's highly questionable whether he ever said it at all or it was a product of Roman myth building...historians of the Roman period were paid by imperial families to write history of their families the way they saw it, it was unhealthy to be honest as a historian in Rome...
most likely, even one of his historians Suetonius doubts he said ever said it... Shakespeare would've have picked it up from Suetonius, and felt free to twist Suetonius's doubts into a definitive quote...Shakespeare/Hollywood, creative writing in the acting business hasn't changed much over 500 yrs......
I'd like to disagree a bit here, e.g. Tacitus was not paid to write "friendly history" for rich families; at least this is the first time I've heard of this. In fact, today's historians usually consider him "imperial-critical." I'm not quite sure if we can assume that Suetonius was paid by Caesar's family to write what he wrote. The Julio-Claudian Dynasty was no more when he wrote his biographies. Cassius Dio, as most Roman authors, wrote mostly about events that took place some, as you mentioned, 100 years (and in his case even more) prior to his time and I haven't read anything about him being paid/instructed/urged to write in favour of the imperial family. He even criticised imperial powers, "kingdom of gold to one of iron and rust." I'd say in the case of Livy and Velleius Paterculus, it's save to say they were very closely affiliated to the emperor's family. Back to original topic: I've heard many nationalistic Turks claiming that Hitler, when one of his generals proposed to attack Russia via Turkey and the Caucasus, said, "Even if we invaded Turkey with 200,000 tanks, we would get out with only 2." I have yet to find confirmation for this, but it sounds too "made-up" anyway.
