A surgical circular stapler, comprising: a staple cartridge, comprising: a cartridge body defining a flat annular deck surface, the cartridge body further comprising: an inner annular row of staple cavities; and an outer annular row of staple cavities positioned radially outward with respect to the inner annular row of staple cavities; at least one first staple positioned within each staple cavity in said inner annular row, wherein each said first staple comprises a first crown and a pair of first legs (4434, 4436) extending from the first crown and defining a first unformed height; and at least one second staple positioned within each staple cavity in said outer annular row, wherein each said second staple comprises a second staple crown and a pair of second legs (4454, 4464) extending from the second crown and defining a second unformed height that is equal to said first unformed height; and wherein said surgical circular stapler further comprises: an anvil movably supportable relative to said staple cartridge and comprising: a first staple forming portion located a first forming distance from said annular deck surface; and a second staple forming portion located a second forming distance from said annular deck surface that differs from said first forming distance; characterised in that the staple cartridge further comprises: a plurality of deck features (4416, 4418) protruding from said flat annular deck surface; and an upstanding outer annular rim extending upward from said flat annular deck surface. a staple cartridge, comprising: a cartridge body defining a flat annular deck surface, the cartridge body further comprising: an inner annular row of staple cavities; and an outer annular row of staple cavities positioned radially outward with respect to the inner annular row of staple cavities; at least one first staple positioned within each staple cavity in said inner annular row, wherein each said first staple comprises a first crown and a pair of first legs (4434, 4436) extending from the first crown and defining a first unformed height; and at least one second staple positioned within each staple cavity in said outer annular row, wherein each said second staple comprises a second staple crown and a pair of second legs (4454, 4464) extending from the second crown and defining a second unformed height that is equal to said first unformed height; and a cartridge body defining a flat annular deck surface, the cartridge body further comprising: an inner annular row of staple cavities; and an outer annular row of staple cavities positioned radially outward with respect to the inner annular row of staple cavities; an inner annular row of staple cavities; and an outer annular row of staple cavities positioned radially outward with respect to the inner annular row of staple cavities; at least one first staple positioned within each staple cavity in said inner annular row, wherein each said first staple comprises a first crown and a pair of first legs (4434, 4436) extending from the first crown and defining a first unformed height; and at least one second staple positioned within each staple cavity in said outer annular row, wherein each said second staple comprises a second staple crown and a pair of second legs (4454, 4464) extending from the second crown and defining a second unformed height that is equal to said first unformed height; and wherein said surgical circular stapler further comprises: an anvil movably supportable relative to said staple cartridge and comprising: a first staple forming portion located a first forming distance from said annular deck surface; and a second staple forming portion located a second forming distance from said annular deck surface that differs from said first forming distance; a first staple forming portion located a first forming distance from said annular deck surface; and a second staple forming portion located a second forming distance from said annular deck surface that differs from said first forming distance; characterised in that the staple cartridge further comprises: a plurality of deck features (4416, 4418) protruding from said flat annular deck surface; and an upstanding outer annular rim extending upward from said flat annular deck surface. a plurality of deck features (4416, 4418) protruding from said flat annular deck surface; and an upstanding outer annular rim extending upward from said flat annular deck surface.