Quintilian, Institutio Oratoria, Book 6
Harold Edgeworth Butler, Ed.

[14] Those who have given a careful study to the arguments that are likely to be produced by their opponents or the replies which may be made by themselves are almost always ready for the fray. There is, however, a further device available which consists in suddenly introducing into the debate arguments which were deliberately concealed in our set speech: it is a procedure which resembles a surprise attack or a sally from an ambush. The occasion for its employment arises when there is some point to which it is difficult to improvise an answer, though it would not be difficult to meet if time were allowed for consideration. For solid and irrefutable [p. 511] arguments are best produced at once in the actual pleading in order that they may be repeated and treated at greater length.