During this period, the laboratory is working at full capacity and reaches its fullest expression. His sonatas —the Waldstein and even the “Kreutzer” Violin Sonata—, together with the Razumovsky Quartets, become the engineering required to sustain the monumental scale of the Eroica and the driving force of the Fifth. Behind each symphony lies preparatory work: at the piano, a search for power; in the quartet, for cohesion. The personal becomes epic: the piano rehearses the “impact”, while the quartet rehearses the “tension”.