Now that we've gotten past the Hanukkah Channuka Chanukah Hannukah video links, I've decided to post a lot of Sondheim video links. Some will be him being interviewed and I'll try to minimize the number in which he tells the story about Oscar Hammerstein telling him his first play was terrible, which he got trapped into telling almost every time he was interviewed. Some will be folks singing his praises or, better still, his songs.
Here's fifteen minutes of him being interviewed on The Mike Douglas Show in 1977. In those minutes, he mentions that when he and his collaborators were working on A Funny Thing Happened on the Way to the Forum, their "dream cast" — not that they had any delusions they could get all these people — was as follows: Phil Silvers as Pseudolus, Danny Kaye as Hysterium, Bert Lahr as Senex, Buster Keaton as Erronius and Zero Mostel as Marcus Lycus.
They wound up with Zero as Pseudolus. Mr. Mostel repeated that role in the movie where he was joined by Silvers as Marcus Lycus and Keaton as Erronius. As Sondheim notes, Mostel was playing Silvers' part and vice-versa.
He also gives a neat little explanation of the song, "Send in the Clowns" and (of course) he tells the story about how Oscar Hammerstein told him his first play was terrible…