“[I]t must be remembered that the law-forms used by the Romans had their origin in times when writing was neither easy nor common. It is not surprising, therefore, that among them a form of spoken words, a verbal contract, should hold the place which among us is occupied by written notes. This form …stipulatio — was of a very simple character, consisting only of a question asked by one party, and an answer returned by the other …. Such forms as Spondesne mihi decem aureos dare (do you engage to give me ten aurei, or gold-pieces): answer, Spondeo (I engage) ….” James Hadley, Introduction to Roman Law 210 (1881).
“The oldest Roman contract was the stipulatio, an oral promise made by an answer to an immediately preceding question, with the promisor using the same verb. The contract was unilateral. Only one party, the promisor, was legally liable, and he was bound strictly by the words used.” Alan Watson, Ancient Law and Modern Understanding 96 (1998).