Discovery did not exist at common law, but its availability in equity attracted litigants in actions at law (legal proceedings in the common law courts). They began to file bills in equity to obtain discovery in aid of actions at law. This led to another innovation in the mid-15th century: the bill to perpetuate testimony of a potential witness. This was for witnesses whose advanced age or poor health implied they would not survive to testify at the trial of an action at law. In this type of proceeding, the parties merely pleaded written interrogatories which a master (in or near London) or a lay commissioner (outside of London) would read out loud to the witness in a closed proceeding without parties or counsel present. The witness's oral answers were written down by the master or lay commissioner in summary form as if they had been delivered as a single continuous narrative (rather than as responses to discrete questions); the actual sequence of questions and answers was not transcribed verbatim like a modern deposition. The resulting document was then sealed and not revealed or "published" (in the terminology of the time) to parties or counsel until shortly before the trial in which it was to be used.