This was because the core vassals of the Asano clan came together during the time of Makabe Domain, Hitachi Province - the first domain formed with a Daimyo - before its transfer to Ako (its territory spread over Makabe County, Tsukuba County and Nihari County, Ibaraki Prefecture) and the time of Kasama Domain after its territory change and increase in property (its territory stretched to Kasama City, Ibaraki Prefecture and former land of Makabe Domain).
浅野氏の家臣団の中心は赤穂に転封される前の大名として初立藩した常陸国真壁藩（茨城県真壁郡・筑波郡・新治郡一帯を所領とする）と加増移封後の笠間藩（茨城県笠間市と旧真壁藩領を所領とする）時代に形成されているためである。