[...]tellers, was first written down in the monasteries. Unfortunately, not a single tale, only two or three poems, have come down to us from these early centuries in contemporary manuscripts. In Ireland nearly all old MSS. were destroyed during the Viking terror which burst upon the island at the end of the eighth century.[1] But, from the eleventh century onward, we have an almost unbroken series of hundreds of MSS. in which all that had escaped destruction was collected and arranged. Many of the tales and poems thus preserved were undoubtedly originally composed in the eighth century; some few perhaps in the seventh; and as Irish scholarship advances, it is not[...].
Various is the correct author for any book with multiple unknown authors, and is acceptable for books with multiple known authors, especially if not all are known or the list is very long (over 50).
If an editor is known, however, Various is not necessary. List the name of the editor as the primary author (with role "editor"). Contributing authors' names follow it.
Note: WorldCat is an excellent resource for finding author information and contents of anthologies.