Seite - 256 - in The Power of Urban Water - Studies in premodern urbanism

256 RainerSchreg River, but the huge building programme established timber rafting on theNeckar even down- streamofTübingen.Theavailabilityof long logs triggeredchanges in theregionalchurcharchi- tecture, when the basilica typewas replaced by hall churches requiring bigger roof construc- tions.29 Unintendedeffects of urbanisationonhydrology and landscape To illustrate the possible interactions between urbanisation and hydrology, the Swabian Alb provides a valuable example, even ifmanyquestionsare still open. TheSwabianAlb is akarst landscape, where there was travertine formation, especially in the valleys along the northern bluff during theHolocene. Travertinedeposits oftenwere several tensofmetres thick and they formed terraces, swamps and even lakes within the valleys (Fig.9). In prehistoric times and even in theMiddleAges,manyvalleys remainedhardlyusable. Theold traffic routes couldnot use the lower gradient in the valleys, but had to surmount the steep slopes on the bluff of the Albdirectly.30 This situation explainswhyarchaeological sites, suchas the late IronAgeoppi- dum at Heidengraben31 or the migration period hillfort at Runder Berg, both close to Urach, were situatedatwhat are today rather remoteplaces. Fig. 9:Romanand medieval traffic lines in thekarst landscapeof the SwabianAlb. Holocene travertine blockedmany valleys at thenorth- ernbluff of theAlb. 29 Marstaller 2009;Marstaller 2012. 30 Schreg 2009d; Schreg 2009e. 31 Stegmaier–Wahr 2009.