Theodore I Palaiologos in the context of "John V Palaiologos"

During the late Middle Ages, the two cities of Argos (Greek: Άργος, French: Argues) and Nauplia (modern Nafplio, Ναύπλιο; in the Middle Ages Ἀνάπλι, in French Naples de Romanie) formed a lordship within the Frankish-ruled Morea in southern Greece.

Following their conquest in 1211–1212, the cities were granted as a fief to Otto de la Roche, duke of Athens, by Geoffrey I of Villehardouin, prince of Achaea. The lordship remained in the possession of the de la Roche and the Brienne dukes of Athens even after the conquest of the Duchy of Athens by the Catalan Company in 1311, and the Brienne line continued to be recognized as dukes of Athens there. Walter VI of Brienne was largely an absentee lord, spending most of his life in his European domains, except for a failed attempt in 1331 to recover Athens from the Catalans. After his death in 1356 the lordship was inherited by his sixth son, Guy of Enghien. Guy took up residence in Greece, and in 1370–1371 Guy and his brothers launched another, also failed, invasion of the Catalan domains. When Guy died in 1376, the lordship then passed to his daughter Maria of Enghien and her Venetian husband Pietro Cornaro, who would also reside there until his death in 1388. The lordship became a de facto Venetian dependency during this period, and shortly after his death, Maria sold the two cities to Venice, where she retired. Before Venice could take possession, Argos was seized by the Despot Theodore I Palaiologos, while his ally, Nerio I Acciaioli seized Nauplia. The latter city was soon captured by Venice, but Argos remained in Byzantine hands until 1394, when it too was handed over to Venice.

Nerio I Acciaioli or Acciajuoli (full name Rainerio; died 25 September 1394) served as the de facto Duke of Athens from 1385 to 1388 and ruled uncontested until his death in 1394. Born into a family of Florentine bankers, he became the principal agent of his influential kinsman Niccolò Acciaioli in Frankish Greece in 1360. He acquired extensive estates in the Principality of Achaea, which he administered independently of the absent princes. In 1374 or 1375, he hired mercenaries and captured Megara, a strategically significant fortress within the Catalan-ruled Duchy of Athens. His forces invaded the duchy again in 1385, driving back the Catalans to the Acropolis, which they were ultimately compelled to surrender in 1388.

Nerio and his son-in-law, Theodore I Palaiologos, Despot of the Morea, invaded the Lordship of Argos and Nauplia in the Peloponnese. Nerio seized Nauplia, but the Venetians soon expelled his troops from the town. In 1389, he was captured by the Navarrese mercenary commander Pedro de San Superano, and released only after pledging to support the Venetian effort to take Argos from Theodore. As security for this promise, he ceded parts of his domains to Venice, though he failed to persuade his son-in-law to surrender Argos. In 1390, Nerio's forces captured the Duchy of Neopatras from the Catalans, but the Ottoman sultan Bayezid I conquered the territory in 1393, after which Nerio paid him an annual tribute for Athens. On 11 January 1394, King Ladislaus of Naples, who claimed suzerainty over Frankish Greece, invested Nerio with the Duchy of Athens. In his last will, Nerio divided his possessions among his younger daughter, Francesca, his illegitimate son, Antonio, and the Church of Saint Mary (the Parthenon) of Athens.