I think the orb and cross was originaly a Eastern Roman (Byzantine) symbol of Christs supremacy over earthly things, and then adopted elsewhere and reinterpreted as it spread. 
 I might be misremembering this but I think in the Sudan it is referred to as the "drum". There is quite a nice series of  posts about these reinterpretations dotted about the kaskara and takouba threads.
		 
		
		
		
		
		
		
		
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