The standard interview process for the 3-year Classics course consists of two interviews, one at your chosen college and another at a random one. I applied to Clare, so had one interview there and the other at Churchill. According to my DoS, the second interview is meant to increase your chances of success if you're pooled: it gives the university more information about you, and gives you two attempts. It doesn't matter where your secondary interview is. For example, I was no more likely to be pooled to Churchill rather than another college. They only use the secondary interview to gather more information about you.

Both interviews lasted around 20 minutes to half an hour. There were two interviewers at my Clare interview, and just one at Churchill. Since I was applying to Clare, I also had to do a translation test. It lasted one hour and consisted of a short passage of Latin. Some colleges don't require an additional test, and others have different types of tests.

Both interviews were roughly the same type - I was given some Latin to look over, and the interviewers put me on the right track when I got stuck. Then we discussed some topics that had come up in the passage, as well as some from my personal statement.

Reading through my personal statement and books, and coming up with practice questions for myself, helped me the most. It allowed me to focus my reading and prepare for the interview style!

Good luck!