The symbolic equation slowly emerged during the course of the sixteenth century as a new mathematical concept as well as a mathematical object on which new operations were made possible. Where historians have of- ten pointed at Francois Viète as the father of symbolic algebra, we would like to emphasize the foundations on which Viète could base his *logistica speciosa.* The period between Cardanos *Practica Arithmeticae* of 1539 and Gosselins *De arte magna* of 1577 has been crucial in providing the necessary build- ing blocks for the transformation of algebra from rules for problem solving to the study of equations. In this paper we argue that the so-called second unknown or the *Regula quantitates* steered the development of an adequate symbolism to deal with multiple unknowns and aggregates of equations. Dur- ing this process the very concept of a symbolic equation emerged separate from previous notions of what we call co-equal polynomials.