If I understand correctly, we are looking at how the presence of large fortifications might impact the political institutions developed by (or imposed upon) a given community in Medieval Europe.

The first and most important thing I would bring up is that Medieval Europe was a place where political institutions existed in a much more immature state than we might be used to in our modern liberal (Western) conception of what government and politics looks like. We will have to wait till the Enlightenment for the first written constitutions to appear in Europe, and even when things like city treaties or charters existed, there was no guarantee that these charters would grant uniform rights or institutions across communities (even when granted by the same monarch). Some communities might have large and complex decision-making institutions, while other might be highly dependent on the decisions of a monarch or ruler. These institutions can exist on a spectrum, with responsibilities that could and interact and even overlap. Relationships between institutions could range from destructive to constructive, with power fluctuating from one institution to another triggered by a spectrum of events ranging from hostile confrontation to peaceful collaboration. The study of medieval politics, and medieval political thought, is fun for this reason: while influenced by broad trends and overarching themes, institutions tend to be an immediate product of their surroundings (I can’t be the only one who defines “fun” this way, can I?).

The medieval period lay down the bones of what would become the nation-states of Europe. The process of laying out these bones, however, was not linear not was its outcome a foregone conclusion: the “Politics of Land” which characterized the broad system-level changes in Medieval Europe are awkward and inefficient. They are especially difficult to reconcile with Europe’s cities and their institutions.

City charters more often than not merely recognize what already existed: Many cities in Mediterranean Europe and beyond trace their origins to the Roman Empire (if not earlier) and their council-based institutions trace their origins to the “Senatorial” style of government exported by the Romans. Thus we have a clear conflict between collegiate, urban-focused institutions of the cities, and the land-based institutions of the emergent medieval monarchies, whose recognition of city charters was one of many efforts at reconciling this sometimes uncomfortable coexistence.

However, cities might themselves appeal to a monarch to guarantee rights and privileges against the encroachment of a local aristocrat, and a monarch might very well be happy to back the city against aristocrats who might be garnering resources to challenge their authority. So cities and monarchies were not necessarily natural enemies. While tensions did sometimes emerge, there is no broad trend of urban power conflicting with monarchal power except in 12th century Italy (although individual urban communities might come into conflict with a monarch, I am not aware of any other systemic conflict to this end).

In 12th century Italy cities and monarchs did come into serious conflict, and a factor was certainly two ends of the Medieval political spectrum interacting: a monarchy coming from a background of having interacted with particularly land-based institutions, colliding with cities that had remained particularly close to their ancient roots and autonomies. But there were very many other factors in play too: the monarchy in question, the Holy Roman Empire, relied on outdated constructs of “Empire” to justify its right to rule Italy (notions which the Italians themselves entertained, as long as the Emperor stayed on the other side of the Alps) and physical distance between the Imperial seat of power and the Italian cities is also a factor that cannot be discounted.

Was the presence of fortifications a boon to Holy Roman Empire (and it’s Emperor, Frederick II) in its attempt to subjugate Italy? Not really. Those cities that were closest to the emperor mostly did so out of choice, having sided with the Empire in an attempt to protect themselves against large and aggressive neighbors, or due to social and political ties to the Emperor or (more commonly) the Imperial Administration. And in these communities themselves, there could be political factions embracing the imperial cause with varying degrees of enthusiasm, further complicating the factors involved. Fortifications actually come into play more significantly in those communities who instead opposed the Empire, with large city walls in Milan, Bergamo, and Brescia, along with fortresses like Alessandria, allowing these communities to defend against imperial encroachment. It is telling that often, even when a city surrendered to the Emperor the fortifications were dismantled.

I would also point out that there is a difference between a “Castle Town” and a “Town with a Castle.” All sorts of fortifications might exist in a medieval city: any important dynasty who participated in urban politics through the ordinary councils and institutions might still construct large fortified homes for themselves (indeed, in times of unrest this was the sensible thing to do). Urban institutions themselves might also construct fortified seats (as the Bolognese did with the Palazzo d’Accursio or the Venetians with the first version of the Doge’s Palace) and when a ruler constructed an urban fortress, they nonetheless continued to contend with local forces which might be entrenched in both institutional and physical fortifications (as the Visconti of Milan had to contend with the citizens of the city of Milan, even after constructing the Castle at Porta Giovia, more commonly known today as “Castello Sforzesco”).

A “Castle Town,” on the other hand, more commonly refers to a town that springs up in and around a fortified manor house. These communities are often rural, and typically were very very small. The local castellan in a “Castle Town,” be he the landholder or his appointee, typically administered the use of capital like grain mill, ovens for baking bread, maybe something like like an olive press, and most importantly, store rooms as well as cellars to age wine or beer. While the communities that sprung up around a castle could grow, attract new residents, and even become thriving towns, very few (certainly none that I know of) developed into towns where elaborate institutions could grow to challenge the power of the “invested” authority.

So to sum up, I would say that in urban spaces, the construction of fortifications followed the relationship between institutions, and not the other way round.