In May of 1935 Einstein published with two co-authors the famous EPR-paper about entangled particles, which questioned the completeness of Quantum Mechanics by means of a gedankenexperiment. Only one month later he published a work that seems unconnected to the EPR-paper at first, the so called Einstein-Rosen-paper that presented a solution of the field equations for particles in the framework of general relativity. Both papers ask for the conception of completeness in a theory and from a modern perspective it is easy to believe that there is a connection between these topics. We question whether Einstein might have considered that a correlation between nonlocal features of Quantum Mechanics and the Einstein-Rosen bridge can be used to explain entanglement. We analyse this question by discussing the used conceptions of "completeness", "atomistic structure of matter", and "quantum phenomena". We discuss the historical embedding of the two works and the context to modern research. Recent approaches are presented that formulate a EPR=ER principle and claim an equivalence of the basic principles of these two papers.