An exam board's decision to drop its ancient history A-level is symptomatic of "the general dumbing-down of Britain", the Conservatives have said.
Interest in the Persian Wars is said to be high
OCR - the last to offer the subject - said revised A-level courses would offer a better range of qualifications.
Elements of ancient history will be in a new classical civilisation A-level.
Shadow education minister Boris Johnson said: "You might as well say you can learn English history through the study of English language and literature."
Mr Johnson - who presented a BBC TV series on the Roman Empire - said: "The birth of Athenian democracy, the transition of Rome from republic to empire: these were critical events in the shaping of our civilisation.
"How can we understand ourselves if we cut ourselves off from our past?
"You can't just subsume the study of ancient history into the study of classical civilisation."
Mr Johnson, president of the Joint Association of Classical Teachers, added: "If we lose ancient history A-level, we lose yet another battle in the general dumbing-down of Britain."
It was, he said, "a tough, rewarding, crunchy subject" giving way to "the softer option".
It was also perverse, given the immense interest in the Persian Wars, and the success of the film 300.
A spokesperson for the board said it remained committed to classics and was the only board still offering "a comprehensive suite of A-levels".
"It is designed to allow classics to flourish over the next decade meeting the needs of schools and colleges - and matches the revised Qualifications and Curriculum Authority subject criteria for classics," he said.
"OCR has consulted widely among examiners, teachers, professional associations, universities and those delivering the existing specifications.
"We've listened to their views and developed a new suite of classics qualifications based on their feedback."