What challenges did cities face as a result of their rapid development?

How to sanitise (human waste) and where to bury the dead.

The primary is infastructure and infrastrucrure management both are an ongoing process for the civic social wellbeing.

Earliest are basics health sanitation as in earliest history large populaces are prone towards pandemic. Secondly would be security such as police and judicial system. Third physical system sustainability such as roads transporting people and goods that enable commerce or emergency evacuation. These three are essential as enabling people live upon such dense population.

Finally, the management these infrastructures the most primitve is a mayor or organizer. This would include agreed funding services, budget repairs/services and negotiating agreements/disputes upon intrests or resources allocation. That best operate a city for their residents short-term requirements and long-term stability.