Institutio Oratoria

Consequently in view of the uncertainty involved, there is need for careful inquiry with a view to discovering the character of the witness against the accused and what are his motives for hostility and what its extent: and all such points about the witness should be set forth in advance and disposed of, whether we desire to represent the evidence against the accused as instigated by hatred, envy, bribery or influence. Further, if our opponents bring forward only a small number of witnesses, we must attack them on that head; if on the other hand they produce an excessive number, we must accuse them of conspiracy: if the witnesses are persons of inconspicuous rank, we must minimise their importance, while if they are powerful, we shall accuse our adversaries of bringing undue influence to bear.