Anachronisms are things placed out of kilter with respect to time. It’s unlikely many Roman chariot racers wore a wristwatch, to pick a famous example. It is (relatively) easy to avoid anachronistic objects like wristwatches.
A more insidious problem is anachronistic phrases: set piece sayings heard every day in modern life and embedded in our DNA, but which you could not possibly hear from a story character.
The knowledge that I will be flayed alive by my readers if they find one causes me to be cautious about the stock phrases that come so easily to the fingertips. Since I am writing in Classical Greece, you shouldn’t expect to hear too much Shakespeare from my characters. No problem, you think? All I have to do is avoid phrases like, "To be, or not to be," and, "Friends, Romans, countrymen?" Think again. The number of routine, daily phrases originating with Shakespeare is mindboggling.
There can be no method in my madness. I can't play fast and loose with my characters, stand on ceremony or make a virtue of necessity. My hero may be a tower of strength, but I daren't say so, or I'll be in a pickle. My victims may be dead as a doornail as the result of foul play, but it's a forgone conclusion I'll be a laughing stock if any of these phrases slip past me into a book.
I am not allowed to use a single one of them, neither those, nor many more. It's enough to make a writer wish the ms would vanish into thin air so he could wash his hands of the whole thing and say good riddance to the problem.
Alright, wash his hands is biblical, but don't get me started on that one, because those common phrases are forbidden too.
Ironically, I can't even say it's all Greek to me.
The subtlety of this goes beyond your wildest nightmares. Here’s my favorite example. I love this example, it really takes the cake.
There it is: that takes the cake!
No, it’s not Shakespeare. It’s Aristophanes. He invented the phrase for his play The Knights, which he wrote in 424B.C. to satirize the Athenian politician Cleon. My stories begin in 460B.C. Out by 44 years. As Maxwell Smart would say, missed by that much! ...damn, I can’t use that one either.