When was the last time there was a landlocked body of water bigger than the Caspian? Was it the Mediterranean before it dried into small lakes? What was the biggest one before that?
The Tethys, which was previously an ocean, became landlocked by the Indian subcontinent to form a massive body of water before the Indian plate collided with the Euarasian to form the Himalayas (about 250-400 Ma).

I don't see any visuals on the Tethys as a sea (as opposed to when it was an ocean) widely disseminated on the web. Here's an approximate diagram from my memory of a textbook: