IIRC.. it formed twice..., and was flooded twice. (Hence the great salt deposits under the med now...)
The Med has completely dried out at least 40 times. The last time it completely dried was 5 million years ago. This information is from Ryan & Pittman's book that SunkenCiv posted in post #14.
Now, it is my suspicion that the Med has become severely dessicated a number of times since then but not completely dry....maybe as recent as about 8,000 years ago, prior to the salt water flooding of the Black Sea..