eram eras etc
>I suppose the stress is always on "e" in these words.
No. In eramus and eratis the stress shifts according to regular rules to
the long /a:/. It is this stress shift that causes the "123-6" pattern of
many irregular verbs in the Romance languages (where the "we" and
"you-plural" forms have a different vowel, or differ in some other way,
including suppletion, from other forms.)
Alos note the forms esse and est with long /e/, from a different stem,
meaning "to eat". e.g. Horace: si quid est animum = if anything is eating
your mind. Long vowel, e:st, not est.
Peter