In polysyllables there was a secondary stress on the alternate vowels.
The syllables "soul, Merman" are respectively cases of primary stress, secondary stress, and no-stress.
In Anglo-Saxon verse the combination of a primary stress, a secondary stress, and an unstressed syllable, is a recognized type.
If the thesis in either foot is the second part of a compound it receives, of course, a secondary stress.
The secondary stress in E1 falls frequently on a short syllable, as in D1.
These are nouns and have the stress on the antepenultima, which in Latin bore the secondary stress.
Whether the penultima has more than a secondary stress is a matter of dispute.