War and armed conflict is, intrinsically, highly disruptive. In addition to the confrontations between armed forces, there are a cascade of other activities, actions, and decisions that disrupt everything around an army in combat or on the move. Some of these are a natural consequence any large group of people: men get hungry and thirsty, and if a campaign extends into the winter, men will need to be clothed and housed. Other considerations are strategic: if it is unfeasible to occupy fortification, it it probably best that it be destroyed. Others still are a little bit of both: Raiding a grain silo, slaughtering livestock, and trampling harvests are measures through which an army can feed itself, but also measures through which an adversary's resources can be whittled down, impacting ability and willingness to carry on the struggle. What this all means is that it is very difficult for anything resembling ordinary life to continue in a medieval warzone, let alone during a siege.

There are, of course, caveats and exceptions. Venice was famously unsuccessfuly besieged in the carolingian era; chroniclers narrate that in order to prove a point, the Venetians pelted the Franks on the shores of the lagoon with bread. Indeed, a maritime city is particularly difficult to besiege without a navy, and this fact was a central component of the Byzantine Empire's strategy in the Lombard Wars.

But generally, urban communities did their utmost to avoid a siege. Terms could be reached by which a city would be spared in exchange for supplies (or gold). A city could preemptively surrender, allowing an occupying army to enter in exchange of guarantees of good order. A political faction within the city might even side with the aggressor, hoping to bolster their own prestige and influence as pressure mounted on decision-makers to guarantee safety. In twelfth-century Italy, when Kaiser Frederick (called Barbarossa by the Italians) sought to impose imperial dominance, some cities which in a first moment sided with the Empire later sided against him as different members ruling councils with different interests and opinions rose and fell in influence. Verona was the most significant city to "flip," but so did several others, including Cremona, which had been a staunchly pro-imperial community at the conflict's breakout.

Kaiser Frederick Barbarossa's campaign in Italy was driven by the unique relationship between Italian communities and the empire, and has a lot of interesting examples of sieges. Indeed, unlike his ancestor Otto who brought Northern Italy in the fold of the Germanic empire without fighting a single pitched battle (let alone a siege) Barbarossa would face an increasingly entrenched opposition that would lead him to make extensive use of siege warfare. A common theme in Frederick Barbarossa's military tactics, by choice or necessity, is his insistence on the demolition of city walls for capitulating cities. The presence of well-developed fortifications was a precondition for a community to hold out against him.

But even the most imposing fortifications could not insulate a city from the ravages of war, or allow life to continue uninterrupted. While all cities are intimately tied to the hinterland that supplies them, dependence on the surrounding territory was very evident in the siege of the largest city in Northern Italy (and one of the largest in Europe): Milan. Indeed, Milan's fortifications were some of the most imposing in Europe: two rings of fortifications, each with a wide moat (which turned into a marsh on the city's southern side, doubling as a harbor in times of peace) and to boot, three rivers supplying the city freshwater.

But the Emperor didn't even need to encircle the walls and drain the moats of Milan in order to disrupt life in the city and drain its resources. He sat a few miles downriver in Pavia, a town which had always been one of his staunchest supporters, and focused on securing the submission of communities on bridgeheads over the Adda and Ticino rivers, to the east and west of the city respectively. Como, another sympathetic city to the north, barred the mountain passes out of Lombardy, while Piacenza, a city to the south, watched over the river Po. The city of Milan was effectively trapped in a crystal box.

A city is only ever as prosperous as its residents. Before the rivers of Lombardy were canalized, Milan was the point where the Olona and Seveso rivers became too shallow and unpredictable for riverboats from the Po, so it was in Milan that merchants and other travelers had to disembark from river boats and board shallow-bottomed barges, or proceed by land. Sure, the Olona and Seveso are not the only waterways flowing from the Alps, since all of Milan's rivals straddle a tributary to the Po: Pavia on the Ticino, Cremona on the Serio, and Lodi on the Adda. All these cities were points where it was convenient for goods to be unloaded from riverboats onto shallower barges or onto oxcarts. In these cities where goods are being unloaded, artisans are more likely to find the raw materials they need, farmers are more likely to find hungry teamsters and longshoremen who will eat their produce, and the conditions are ripe for a city to grow and prosper. There is no single reason why Milan grew so much larger than its peers in Northern Italy; it could simply be that the Roman Emperor Maximilian liked the city so much he moved his palace there, enshrining the city's primacy in Italy. But more likely, when Maximilian moved to Milan the city was already an established supply point for Roman Legions (perhaps the Olona and Seveso were particularly easy to sail up). Or, even with a Roman palace and Roman foundries and grain stores, it is possible that the city did not mature its primacy until after the Roman Empire, when Lombard and Frankish rulers favored the city as their base of operations on the Peninsula. The point is that a multitude of factors combine, with varying and debatable degrees of importance, in order to contribute to a city's growth.

Thus as the Emperor choked the waterways flowing from the city, burnt the surrounding fields, trampled the pastures and slaughtered the livestock in the surrounding countryside, something else also occurred: if its population was immobilized, visitors could not (and would not come) to the city, and the mercantile entrepot of Milan found it had no reason to exist. The Milanese shut the gates, as did their vavasours, but by closing their gates they were keeping more than the enemy out: they were keeping aristocrats from visiting their estates, farmers from bringing their produce to market, and artisans from obtaining raw materials. The ruling council could only send embassy after embassy to the emperor in an attempt to come to terms and allow life to resume as before.

Eventually, the Milanese council unconditionally surrendered. The residents of the city had just enough time to disperse among satellite communities such that chroniclers report the Emperor entered an empty city. On the advice of his Italian supporters, Emperor Frederick gave the order that the vacated city be destroyed. In the nearby fortified boroughs of Baggio, Busto, or in the fortress at Linate or Abbiategrasso, the Milanese could finally attempt to resume life as before. But a city is always the sum of its residents, and some Milanese had already begun plotting their revenge.