This thesis is based on the observation that in the Lake Mälaren region, places with the name Stenby ("stone village") tend to be located next to hillforts. I have researched the occurrence of the place name Stenby with medieval evidence for the name in eastern central Sweden and found sixteen that are located in the Mälaren Valley region. Of these, twelve had a hillfort within one kilometer and eleven were assessed as being from the Migration Period. There is one hilltop settlement in the material: Broborg in Uppland. Of the eleven Migration Period hillforts, ten were located close to Lake Mälaren or had a waterway to Lake Mälaren. Eight of the twelve Stenby places with a hillfort were located in areas that could constitute aristocratic central areas with many sacral placenames referring to Norse Gods and names containing -tuna and -lunda. They are in open landscapes with wide views. Two Stenby hillfort complexes were adjacent to a (nautical) fairway. These findings suggest a central organization within the region.  The only exception from the Migration Period hillfort pattern is in Riala Parish, which has an older bank enclosure. Riala is not situated in an Iron Age central district and lacks a water connection with Lake Mälaren. Of the four Stenby without a nearby hillfort, two lacked close Iron-Age burial grounds and are not certain to be Migration Period settlements. One may be associated with a smaller mountain called Onsberget ("Oden's mountain").