early 13c., "a seat" (as in Siege Perilous
, the vacant seat at Arthur's Round Table, to be occupied safely only by the knight destined to find the Holy Grail, c.1230), from O.Fr. sege
"seat, throne," from V.L. *sedicum
"seat," from L. sedere
"sit" (see sedentary
). The military sense is attested from c.1300; the notion is of an army "sitting down" before a fortress.