8. Perdita Weeks
Having played Mary Boleyn, sister to Henry VIII, on Showtime's The Tudors, Perdita Weeks certainly has experience of the period drama. While her background may also tend towards the Victorian side of history - such as Lost in Austen or the BBC 2011 Great Expectations miniseries - it seems a little unusual that she'd turn down a part in a show as big as Game of Thrones. The role she's rumored to have been offered - that of Edmure Tully's bride, Roslin Frey - is hardly the most glamorous part but better-known actors have taken smaller for the sake of appearing on the show (see further down the list). After the project that won out over Game of Thrones fell through for her, Weeks seems to have been at a loose end - she admits to having rung the show's producers to "beg for back", but having appeared on Downton Abbey creator Julian Fellows' high-profile Titanic early last year (as a lady heiress no less) she seems to be doing pretty well nonetheless.