© Dictionnaire historique de la Suisse. Rédaction Wener Meyrer
The scarcity of the sources written between the IX E and the XII E S. hardly enables us to enter in detail of the cultural, economic and social facts, and obliges us to resort to the archeology or the inductive analysis of more recent sources. Occasional mention, to the IX E S., local leaders, the such count Chadaloh, and grounds belonging to distant abbeys makes foresee the existence of seigniorial structures. With X E S, the area of Basle on the left of the Rhine belonged to the second kingdom of Burgundy. The weakness of the royal power encouraged the formation of noble seigniories, in particular in the Jura, little populated and covered of forests. The transfer of Basle to the emperor Henri II around 1006 and that of Burgundy to the emperor Conrad II in 1033 changed nothing there, although Henri III invested the bishop of Basle of the comtaux rights on Sisgau in 1041.
On the basis of the old soils inherited Antiquity and Early middle ages, the medieval clearings touched little by little the margins of the side valleys and the heights. It was a question of gaining new grounds to be cultivated and colonize, but also, especially in the areas concerned with the counts de Frobourg and in the average valley of Birse, to seek and exploit the iron ore. Often related to the clearings, the strong castles of X E S. (Altenberg, Vorder-Wartenberg, Ödenburg, Zunzgen for example) became the centers of the seigniorial complexes which were formed in the grounds old and new and whose hard copies are increasingly frequent as of the end of the XI E S. the construction of the strong castles knew its golden age to the XIII E S. and ceased to the XIV E. The clearings, the construction of the castles and the formation of the seigniories have as persons in charge of the noble parentèles, of row comtal, whose sources give us the names around 1100 as soon as possible: Saugern-Pfeffingen in the average valley of Birse, the counts de Frobourg, who progress of the southern foot of the Jura towards Sisgau. The counts de Homberg-Thierstein exerted under solicitors the temporal rights of the bishop of Basle. The counts de Rheinfelden had badly known goods and rights; their extinction, before 1100 already, seems to have benefitted the lords from Eptingen, perhaps of free origin and non-ministériale, which built in Sisgau, to the XII E and XIII E S., several small seigniories protected by strong castles (in particular Eptingen, Bischofstein, Wildenstein, Gutenfels, Madeln close to Pratteln). The lords of Ramstein and Rotberg, undoubtedly noble and nonministériaux, had their grounds at the south-western edge of Sisgau.
As of the end of the XII E S., the country minor nobility was also put at the clearings, which involved the construction of many strong castles on the new grounds, such Bärenfels, Scheidegg (Com. Gelterkinden), Schauenburg or Ramlinsburg. At the XIII E S., the urban nobility of Basle started to raise castles in the countryside, such Münchenstein, Angenstein, Landskron (F), Schalberg and Münchsberg (both in the commune of Pfeffingen), which generally only a few arpents concerned, sometimes a village.
The convents of Beinwil-Mariastein, Olsberg and Schönthal, noble foundations of the XII e-XIII E S., played only one part of second plan in the process of the clearings.
The formation of territorial units started in the area of Basle around 1200 with the foundation with the sovereign lords of cities and strong castles. The counts de Frobourg, after having created in Sisgau Waldenburg, Liestal and Neu-Homberg, had to give up towards 1270/1280 their princely ambitions with the bishops of Basle Those affirmed themselves in the average valley of Birse by melting Laufon around 1295. Their territorial policy passed by the transformation into strongholds of the majority of the autonomous seigniories of Sisgau and of the valley of Birse, to the XIII E and the beginning of the XIV E S. But the situation reigning around 1300 does not draw the future cantonal and national borders yet.
The ecclesiastical organization, in particular that of the parishes and the décanats, is known only starting from low Moyen-âge, but essence was to already be in place around the year thousand. Whereas the territory depend on the bishopric then of the town of Basle located on Right Bank of the Rhine concerned the diocese of Constancy, that located on left bank formed part as of the Early middle ages of the diocese of Basle. The décanat of Sisgau understood the parts of the current cantons of Basle-Countryside and Soleure east of Birse, and Rheinfelden, that of Leimental the average valley of Birse, southernmost Sundgau and the basin of Birsig.