The subject probably is Horatius Cocles, the legendary Roman soldier whose heroism saved Rome from capture by the Etruscan forces of Lars Porsenna, who took his stand on a bridge across the Tiber - keeping the Etruscans at bay while the Romans demolished the bridge behind him (Livy 2, 10 and Plutarch 6, 16).
A similar drawing, showing a soldier on horseback fighting a group of foot soldiers as his horse rearing above a prostrate figure shielding himself, is in the Berlin print room (inv. 20636). The Metropolitan preserves a drawing by the Cambiaso school of the same subject as the Berlin one, which depicts the rider in a very similar pose to the one in the Morgan sheet (inv. 87.12.14).
Watermark: yes.
Inscribed at on old mount, at lower center, in pen and dark-brown ink, "dell'istessa man[i]era / de Cambiagi".
Komor, Mathias, 1909-1984, former owner.
Pierpont Morgan Library. Review of Acquisitions, 1949-1968. New York : Pierpont Morgan Library, 1969, p. 136.
Adams, Frederick B., Jr., comp. Eleventh Report to the Fellows of the Pierpont Morgan Library, 1961. New York : Pierpont Morgan Library, 1961, p. 78.