The‘war of the three Johns’–or, to put it another way, the assault and
siege of Constantinople in 1235– 6 – was the defining event of John’s
reign there. It has sometimes been suggested that he redeemed his
relatively lacklustre rule‘[on] the day when he saved [the city] by his
heroism’.^172 However, this view is both too harsh on the reign, and
too credulous about John’s military role. Certainly, he led at least one
cavalry sally from the land walls, scoring a tactical victory that was
doubtless milked for all it was worth to boostflagging morale. If anything
saved Constantinople in 1235, though, it was the timely arrival of a
Venetianfleet, which destroyed Vatatzes’and Asen’s hopes of a‘carefully
co-ordinated dual attack on the city by land and sea’.^173 When the
Venetians had departed for home, however, Vatatzes and Asen
unexpectedly wheeled their forces and invested Constantinople again.
This time, though, they may well have shifted to a‘siege strategy’alone,
since their earlier assaults had proved bloody and unsuccessful. If so,
however, then this was always a long shot, since the sea –three of
Constantinople’s four sides–was where the Westerners were strong.
Reinforcements quickly came in from Venice again, as well as from
Genoa and Pisa. It is also worth mentioning the role of various‘vassal
states’of the Latin empire: duchies such as Athens, which would later
fall into Brienne hands, and the Aegean lordship of the Archipelago. The
greatest of these vassal states was the principality of Achaia (or the
Morea), located in the Peloponnese. The Latin emperors had done much
to secure the loyalty and support of the Villehardouin princes of Achaia.
John was well placed to strengthen the relationship still further, since the
princes were actually of Briennois origin. From the very beginning of
Emperor John’s reign, in fact, Prince Geoffrey II of Achaia had supplied
him with an annuity, said to be worth some 22,000hyperpyra.^174 Now, in
the dark days of 1236, Geoffrey did even more. The combined naval
operation mounted by the prince, the Venetians, the Genoese and the
Pisans proved sufficient to puncture Vatatzes’naval blockade, docking at
Constantinople in triumph. Soon afterwards, Asen abandoned his alli-
ance with Vatatzes, forcing the dispirited Nicaean emperor to lift the
(^172) Adapted from J. Longnon,L’empire latin de Constantinople et la principauté de Morée
(Paris, 1949), 174.
(^173) J. S. Langdon,‘The Forgotten Byzantino-Bulgarian Assault and Siege of Constantinople,
1235 – 1236, and the Breakup of theEntente Cordialebetween John III Ducas Vatatzes and
John Asen II in 1236 as Background to the Genesis of the Hohenstaufen-Vatatzes
Alliance of 1242’,inByzantina kai Metabyzantina,vol.iv:Byzantine Studies in Honor of
174 Milton V. Anastos, ed. S. Vryonis Jnr. (Malibu, 1985), 111.
Alberic of Trois-Fontaines,Chronica, 939; and Perry,John, 166–7.
72 Breakthrough and High Point (c. 1191–1237)