i bought "A new introduction to old norse" and i was reading about the
usage of nouns. but i got a problem. they give an example which
is "Hann sendi þá vestr at leita ǫndvegissúlna sinna" they dont say
why "ǫndvegissúlna" has to be in genetiv

can somebody please tell me why? =)
thank you very much =)

note: ǫndvegissúlna = high-seat-posts
and it is the ending -na in (ǫndvegis)súlna which is genetiv (plural)