Tiling engines and methods for use in a graphics processing system for hierarchically tiling a plurality of primitives. The tiling engine includes: a chain of sorting units comprising a top level sorting unit followed by one or more lower level sorting units, wherein: the top level sorting unit is configured to: determine which of a plurality of regions of a render space each of the plurality of primitives, at least partially, falls within; and for each region a primitive, at least partially, falls within, store an identifier of that primitive in a queue of the top level sorting unit that is associated with that region; and each of the one or more lower level sorting units is configured to: select one or more queues of a preceding sorting unit in the chain to process; for each of the selected queues, determine which of a plurality of sub-regions of the region associated with that queue each of the primitives identified in that queue, at least partially, falls within; and for each sub-region a primitive, at least partially, falls within, store an identifier of that primitive in a queue of the lower level sorting unit that is associated with that sub-region; and an output unit configured to output the primitives identified in the queues of the last lower level sorting unit in the chain on a queue by queue basis.