In this paper, I discuss the importance of fossil fields and traces of ancient agriculture as archaeological source material. Examples from excavations in the Väderstad area in Östergötland, Sweden are given. In the article, I describe and contrast two different methods of excavation: (A) The digging of long trenches through visible features, a method here used as a means of trial excavation but previously often the only method used in the excavation of ancient fields. This method gives at the best a framework for interpretation. Though it does enable dating, the intensity, extent and content of different phases cannot be established with any degree of certainty. (B) The removal of the ancient plough soil over the full extent of the ancient field, a method here used for final excavations. With this method, enough information was acquired for the derivation of a detailed interpretation. The results will be detailed enough to allow comparison of the excavated fields with other categories of excavated monuments and thus give a new perspective on general archaeological problems. The RAÄ 166 site at Hogstads socken is given as an example of this approach.