In early Florentine society, merchants (the popolo grosso) had to find ways to fight off the warring nobles (the grandi), as those nobles saw merchants on a tier below them, and saw fit to destroy what they had.
Thus, the merchants had to hire mercenaries to defend themselves.
Money makes the world go ’round, and it was no different back then. The mercenaries would fight for whoever paid them the highest amount, and so they fought for the merchants.
Eventually, the nobles were forced to leave their countryside estates and move into the city. However, moving into the city doesn’t mean that their worldview changed. In order to gain a higher vantage point and look down upon the rest of the citizens, they built high towers. In addition, many noble families married into rich merchant families, creating a new type of upper class in Florence.
After the nobles and merchants came the artisans and guildsmen, who were able to influence some things in government as long as they had the right connections. They were the middle class, so, although they didn’t have the lavish riches of the upper class, they were able to live comfortable and pursue their trade.
Behind the artisans were the poor, or “popolo minuto“. These were the working poor. Understandably, they weren’t able to accomplish much, but, as they were “unimportant”, the things they did weren’t monitored with much caution unless they did something outrageous.