Explanation: The city of Alexandria in Roman Egypt had a... long history of rioting under the Roman Empire. And generally not against the Roman Empire itself.

Romans generally allowed cities to continue using their own laws to govern their own region, regardless of how far it was from Roman law. One of the 'features' of the privileged Greek colony of Alexandria in Ptolemaic (Greek) ruled Egypt was that it had a system which excluded most of the free population from full rights of the city. 'Greek' citizens of the city, born to two 'Greek' citizens (having one non-'Greek' parent, or an unknown father, would not bestow 'Greek' citizenship) of Alexandria, had full rights - everyone else was second-class or third-class, and with no hope of ever becoming anything else.

This meant that ethnic tensions of this Greek-privileged city in the midst of an Egyptian hinterland and with a large population of provincial immigrants from elsewhere in the Roman Empire, including a longstanding Jewish community, were always... simmering.