Thucydides, Sun Tzu, Livy, Machiavelli, Clausewitz - magic names.
These Masters of War are still read centuries & millennia later.
Thucydides' The Peloponnesian War was the classical text of choice during the two Iraq wars.
And General Colin Powell, famously, had the following quote from the master framed on his State Department desk:
"Of all manifestations of power, restraint impresses men most."
Sun Tzu, Machiavelli and Clausewitz are no less popular.
Why are these authors still relevant?
Because they wrote beautifully - clear, simple sentences that cut to the heart of the issue.
Because they lived what they wrote about. (All were practitioners, with all respect to many contemporary academics.)
Because human nature does not change.
In our consulting work, I see the same chess positions over and over.
Different board, different style of chess piece -- but the same positions.
The greats understand this, which I suppose is what makes them great.
I have image of these old boys shooting the breeze in a bar, regaling one another with stories, the ideas, opinions and insights coming fast & furious.
(I'd love to be the bartender!)