Product Lines evolve out of existing products. In order to evaluate the potential of creating a Product Line from existing products it is necessary to 'mine' their architectures and analyze the commonalities and variabilities across those architectures. To manage the evaluation process in a disciplined way this paper introduces the MAP (Mining Architectures for Product Lines) method. MAP outlines a bottom-up approach for mining the architecture of the existing products, a top-down approach to mapping architectural styles and attributes onto the mined architectures and an approach to analyzing their commonalities and variabilities. It combines well-known architecture reconstruction and Product Line analysis techniques. A case study is presented showing the application of the method and its benefits are outlined.