 After completing general relativity, Einstein long entertained hopes that matter might be described in geometrical terms by a theory unifying gravitation and electromagnetism. But he stoutly and repeatedly resisted proclamations of any reduction of physics to geometry (e.g., 1928: 254; Giovanelli 2013a). Theoretical unification was overriding goal; no special significance would accrue to any successful unifying theory whose physical objects, motions, and interactions are described in geometrical terms (Lehmkuhl 2014). Einstein nonetheless followed both approaches to theoretical unification, that of generalizing Riemannian geometry and by adding extra dimensions. By 1923, Einstein was the recognized leader of the unification program (Vizgin 1985 [1994: 265]) and by 1925 had devised his first “homegrown” geometrical “unified field theories” (Sauer 2014). The first phase of the geometrical unification program essentially ended with Einstein’s “distant parallelism” theory of 1928–1931 (e.g., 1929), an inadvertent public sensation (Fölsing 1993 [1997: 605]). Needless to say, none of these efforts met with success. In a lecture at the University of Vienna on October 14, 1931, Einstein forlornly referred to his failed attempts, each conceived on a distinct differential geometrical basis, as a “graveyard of dead hopes” (Einstein 1932). By this time, certainly, the viable prospects for the geometrical unification program had considerably waned. A consensus emerged among nearly all leading theoretical physicists that while unification of the gravitation and electromagnetic fields might be attained in formally distinct ways, the problem of matter, treated with undeniable empirical success by the new quantum theory, was not to be resolved solely within the confines of classical fields and spacetime geometry. In any event, from the early 1930s, prospects of any type of unification program appeared greatly premature in view of the wealth of data produced by the new physics of the nucleus.