1 Answer

According to WIKIPEDIA, here's a partial answer.  See WIKIPEDIA for more info:

The Confrontation Clause of the Sixth Amendment to the United States Constitution provides that "in all criminal prosecutions, the accused shall enjoy the right…to be confronted with the witnesses against him." Generally, the right is to have a face-to-face confrontation with witnesses who are offering testimonial evidence against the accused in the form of cross-examination during a trial. The Fourteenth Amendment makes the right to confrontation applicable to the states and not just the federal government.[1] The right only applies to criminal prosecutions, not civil cases or other proceedings.
The Confrontation Clause has its roots in both English common law, protecting the right of cross-examination, and Roman law, which guaranteed persons accused of a crime the right to look their accusers in the eye. In noting the right's long history, the United States Supreme Court has cited Acts of the Apostles 25:16, which reports the Roman governor Porcius Festus, discussing the proper treatment of his prisoner Paul: "It is not the manner of the Romans to deliver any man up to die before the accused has met his accusers face-to-face, and has been given a chance to defend himself against the charges." It has also cited Shakespeare's Richard II, Blackstone's treatise, and statutes.[2]