> If Roman Britain was ethnically diverse You probably mean racially diverse -- most Roman soldiers / administrators were ethnically Roman, regardless of race.

> If Roman Britain was ethnically diverse You probably mean racially diverse -- most Roman soldiers / administrators were ethnically Roman, regardless of race. > then what happened to the diversity? Cities have historically been population sinks, not able to replenish themselves without constant population flows from the countryside. If there were non-white people in the cities it might not have left much trace in the population's genes.