This is a valuable article from Histcape (EU project) website by Matthias Ripp World Heritage Officer Regensburg. "CRISIS:AN OPPORTUNITY FOR HISTORIC CITIES - built cultural heritage as a factor of urban resilience" See direct link.
I am indebted to Huib Crijns of 'den Bosch for alerting me to this article.
The importance of the article lies in explaining how historic cities, which have proved their resilience over centuries have features that need to be conserved to maintain future resilience. Town walls and the concentrated town centres exemplified in walled towns are classic cases.