pper ▁and ▁bronze ▁working ▁before ▁their ▁Iron ▁Age . ▁Co pper ▁is ▁quite ▁rare ▁in ▁Africa ▁while ▁iron ▁is ▁quite ▁common . ▁In ▁N ub ia ▁and ▁Eth iop ia , ▁iron , ▁trade , ▁and ▁agricult ural ▁sur pl uses ▁lead ▁to ▁the ▁establishment ▁of ▁cities ▁and ▁civil izations . ▁ ▁The ▁B ant u ▁expansion ▁ ▁Ord in arily , ▁in ▁the ▁sp ars ely ▁populated ▁areas , ▁this ▁same ▁period ▁saw ▁the ▁expansion ▁of ▁the ▁B ant u ▁speaking ▁pe op les . ▁The ▁B ant u ▁expansion ▁began ▁in ▁Southern ▁Cam ero on ▁around ▁ 4 0 0 0 ▁years ▁ago . ▁B ant u ▁languages ▁are ▁spoken ▁there ▁today ▁and ▁there ▁is ▁arch ae ological ▁evidence ▁for ▁incoming ▁Ne ol ith ic ▁far mers ▁in ▁Northern ▁Gab on ▁c . ▁ 3 8 0 0 ▁BC . ▁It ▁is ▁known ▁that ▁B ant u ▁expansion ▁was ▁extremely ▁rapid ▁and ▁massive , ▁but ▁its ▁exact ▁engine ▁remains ▁controvers ial . ▁This ▁period ▁pred ated ▁iron , ▁which ▁appears ▁in ▁the ▁arch ae ological ▁record ▁by ▁ 2 5 0 0 ▁BC . ▁ ▁One ▁of ▁the ▁early ▁exp ans ions ▁of ▁B ant u ▁was ▁the ▁migration ▁of ▁the ▁B ub i ▁to ▁Fernando ▁Po ▁( Bi oko ). ▁They ▁were ▁still ▁using ▁stone ▁technology ▁at ▁first . ▁The ▁difficulties ▁of ▁cutting ▁down ▁the ▁equ atorial ▁forest ▁for ▁far ming ▁have ▁led ▁to ▁the ▁suggestion ▁that ▁the ▁primary ▁expansion ▁was ▁along ▁river ▁valle ys , ▁a ▁hypothesis ▁supported ▁by