The aim of the research is to investigate the work of the Swedish architect Mathias Spihler during the latter half of the 17th century. He was a disciple to the royal architect Jean de la Vallée and became an architect in great demand. Mathias Spihler only achieved an appointment as foreman and engineer. The best known constructions are Kungsholms church in Stockholm and the countryseats of Salsta and Sjöö. A problem connected to the research is that the constructions of Spihler often have been attributed to the famous architect Nicodemus Tessin the elder. Mathias Spihler has rather been apprehended as an underarchitect and organiser than architect in the Swedish architectural history. As a result he has got a position in the shadow of the main architects Jean de la Vallée and Nicodemus Tessin the elder. The aim of the project is to show that Mathias Spihler soon became a self-dependent architect who carried out a large number of buildings. He is also important as a pioneer for architects not connected to a royal appointment.