Our first threshold clustering simulations were performed on crystalline benzene, a system that has been wellstudied within the CSP literature, including in studies into reducing overprediction. Experimentally two forms have been fully characterized: the ambient pressure form I and the high-pressure form III. Other high pressure forms have been proposed but have not yet been conclusively determined. The 100 lowest energy predicted structures, representing an energy cutoff of 7.5 kJ mol -1 from the global minimum and including matches to both experimental polymorphs, were selected from the CSP landscape and simulations ran with two energy lids, first at 2.5 then at 5.0 kJ mol -1 . The results from the threshold simulations show a significant elaboration of the low energy region, the number of unique structures increasing to nearly six times that of the initial set. This filling in of the landscape is a notable benefit of sampling the regions around CSP structures, and augments the necessarily sparser sampling of the CSP method. Moreover, because the space group symmetry is removed before the threshold simulations (to avoid symmetry constraints on the transitions between structures), new structures are located in space groups outside the initial CSP search. For example, the initial CSP for benzene searched 25 space groups. However, using PLATON to add symmetry to the unique structures from the threshold simulations, we find 39 space groups represented. A further consequence of removing the space group symmetry is some of the CSP structures are no longer at minima on the lower symmetry energy surface, hence there are differences between the initial structures before and after the threshold simulations, including a small number of minima coalescing; this is described further in the supplementary information.