Large-scale enterprises struggle with an effective alignment of business processes and IT services with business strategy. While process models play an important role for bridging between strategy and IT, there is a need to systematically organize the huge number of models. Process architecture defines an overarching structure for the organization of processes. However, there is a notable research gap on how process architectures are designed in practice. In this paper we address this problem by integrating insights and approaches from practice. We use Grounded Theory to analyze eleven in-depth interviews we conducted. Further, we present findings from studying documents provided by the interviewees. Our contribution is a conceptual framework about process architecture design, along with a classification of process architecture archetypes found in practice. Our results have strong implications since they demonstrate that process architecture design is more complex and context-dependent than assumed.