One of the daily tasks of an enterprise architect is to prioritize strategic IT projects. To achieve a business-IT alignment, this prioritization needs to be based on business strategies and goals. Therefore, business goals and their traceability to strategic IT projects are relevant for the enterprise architect. However, surpris-ingly little formalisations and reasoning techniques have been developed in the enterprise architecture domain. In this paper we show that the popular goal modelling technique Tropos together with its formal reasoning techniques can support the enterprise architect when prioritizing strategic IT projects. We prove the feasibility of our work with a tool implementation of the proposed modelling language and its corresponding algorithms; and demon-strate their usefulness with the help of an example taken from the enterprise architecture literature.