Adam Clarke on Song of Solomon 1:9

I have compared thee - to a company of horses - This may be translated, more literally, "I have compared thee, to my mare, in the chariots or courses of Pharaoh;" and so the versions understood it. Mares, in preference to horses, were used both for riding and for chariots in the East. They are much swifter, endure more hardship. and will go longer without food, than either the stallion or the gelding.

There is perhaps no brute creature in the world so beautiful as a fine well-bred horse or mare; and the finest woman in the universe, Helen, has been compared to a horse in a Thessalian chariot, by Theocritus. Idyl. 18: ver. 28: - Ὡδε και ἁ χρυσεα Ἑλενα διαφαινετ' εν ἡμιν, Πιειρη, μεγαλη, ἁτ' ανεδραμεν ογμος αρουρᾳ, Η καπῳ κυπαρισσος, η ἁρματι Θεσσαλος ἱππος. "The golden Helen, tall and graceful, appears as distinguished among us as the furrow in the field, the cypress in the garden, or the Thessalian horse in the chariot."

This passage amply justifies the Hebrew bard, in the simile before us. See Jer 6:2.