Verified answer

any half decent grammar book will tell you that verbs which end in -er,

will have -èrent in the 3rd person plural in the Past Historic.

All other verbs take -irent or -urent [no accent on the u or the e there]

regular verbs in -ir, always take the -irent ending. Irregular verbs can take -irent or

-urent, you just need to learn them, but then you will be learning your irregular verbs anyway.

verbs ending in -oir take either - just learn which is which.

Learn être and avoir separately: furent and eurent

If you're having trouble with your verbs, get yourself a copy of Bescherelle, La Conjugaison - every single French verb is in one table or another. It's wonderful.

http://www.laits.utexas.edu/tex/gr/tap10.html