Is Durban really second largest? What about Cape Town, Johannesburg, Pretoria, and Soweto? I could easily be wrong with all the confusion of metropolitan area vs. city proper...
According to population stats, Durban is 2nd largest to Cape Town in 1st. Durban has an approximate population of 3.1mil with Johannesburg having circa 2mil, Soweto 1.7mil and Pretoria 1.6mil. Hope this answers your question.