The legion, in biological classification, is a non-obligatory taxonomic rank within the Linnaean hierarchy.
Taxonomic rank 
In zoological taxonomy, the legion is:
- subordinate to the class
- superordinate to the cohort.
- consists of a group of related orders
Legions may be grouped into superlegions or subdivided into sublegions, and these again into infralegions.
Use in zoology 
Legions and their super/sub/infra groups have been employed in some classifications of birds and mammals. Full use is made of all of these (along with cohorts and supercohorts) in, for example, McKenna and Bell's classification of mammals.
See also 
- ^ McKenna, Malcolm C., and Susan K. Bell (editors). 1997. Classification of Mammals Above the Species Level. New York: Columbia University Press. ISBN 0-231-11013-8