Please tell me more about neighbourhood PMCs in renaissance Italy
It would be my pleasure! (My research into this owes a lot to the excellent Power and Imagination: City-States in Renaissance Italy by Lauro Martines.)
The first thing to note that, unlike the condottieri, these were not private military companies. Rather, the neighborhood military companies (in the sense of a military unit, rather than a profit-making entity) were self-defense organizations formed as part of a centuries-long political struggle for control over the urban commune between the signorile (the urban chivalry)/nobilita (the urban nobility) and the populo (the guilded middle class, who claimed to speak on behalf of "the people").
This conflict followed much the same logic that had given rise to the medieval commune in the first place. Legally, the communes had started as mutual defense pacts between the signorile and the cives (the free citizens of the city) against the rural feudal nobility, which had given these groups the military and political muscle to push out the marquises and viscounts and barons and claim exclusive authority over the tax system, the judicial system, and the military.
So it made sense that, once they had vanquished their enemies and established the commune as the sovereign, both sides would use the same tactic in their struggle over which of them would rule the commune that ruled the city. The signorile and nobilita formed themselves into consorteria or "tower societies," by which ancient families allied with one another (complete with dynastic marriage alliances!) to build and garrison the towers with the knights, squires, men-at-arms, and bravi of their households. These phallic castle substitutes were incredibly formidable within the context of urban warfare, as relatively small numbers of men with crossbows could rain down hell on besiegers from the upper windows and bridges between towers, even as the poor bastards on the ground tried to force the heavy doors down below.
To combat noble domination of communal government, achieve direct representation on the political councils, establish equity of taxation and regulate interest rates, and enforce legal equality between nobility and citizenry, the populo formed themselves into guilds to build alliances between merchants and artisans in the same industries. However, these amateur soldiers struggled to fight on even footing with fully-trained and well-equipped professional soldiers, and the guild militias were frequently defeated.
To solve their military dilemma, the populo engaged in political coalition-building with the oldest units of the urban commune: the neighborhoods. When the cities of medieval Italy were originally founded, they had been rather decentralized transplantations of the rural villages, where before people had any conception of a city-wide collective their primary allegiance was to their neighborhood. As can still be seen in the Palio di Siena to this day, these contrade built a strong identity based on local street gangs, the parish church, their traditional heraldry, and their traditional rivalries with the stronzi in the next contrade over. And whether they were maggiori, minori, or unguilded laborers, everyone in the city was a member of their contrade.
As Martines describes, the populo both recruited from (and borrowed the traditions of) the contrade to form their armed neighborhood companies into a force that would have the manpower, the discipline, and the morale to take on the consorteria:
"Every company had its distinctive banner and every house in the city was administratively under the sign of a company. A dragon, a whip, a serpent, a bull, a bounding horse, a lion, a ladder: these, in different colors and on contrasting fields, were some of the leitmotifs of the twenty different banners. They were emblazoned on individual shields and helmets. Rigorous regulations required guildsmen to keep their arms near at hand, above all in troubled times. The call to arms for the twenty companies was the ringing of a special bell, posted near the main public square. A standard-bearer, flanked by four lieutenants, was in command of each company."
To knit these companies organized by neighborhood into a single cohesive force, the lawyers' guilds within the populo created a state within a state, complete with written constitutions, guild charters, legal codes, legislative and executive councils. Under these constitutions, the populo's councils would elect a capitano del popolo, a professional soldier from outside the city who would serve as a politically-neutral commander, with a direct chain of command over the gonfaloniere and lieutenants of the neighborhood companies, to lead the populo against their noble would-be overlords.
And in commune after commune, the neighborhood companies made war against the consorteria, taking the towers one by one and turning them into fortresses of the populo. The victorious guilds turned their newly-won military might into political hegemony over the commune, stripping the nobilita of their power and privilege and forcing them either into submission or exile. Then they directed their veteran neighborhood companies outward to seize control of the rural hinterland from the feudal aristocracy, until the city had become city-state.
(Ironically, in the process, the populo gave birth to the condottieri, as the nobility who had lost their landed wealth and political power took their one remaining asset - their military training and equipment - and became professional mercenaries. But that's a story for another time...)