The Byzantine leadership had no real plan, since the idea that the Crusaders should attack them came as a surprise. Nevertheless, the Byzantine army had a long tradition of what might, in modern terms, be called contingency strategies. These were based upon the idea that all means should be used to weaken the enemy, to achieve peace, and to obtain information. Battle was a last resort, and there is no reason to suppose that attitudes had changed by the time of the Fourth Crusade.
Since the Byzantines saw their emperor as the supreme overlord of the Christian world and ruler of a Roman Empire that had been blessed by God, his duty was ‘to guard and secure by his ability the powers that he already possesses’. Anything was permissible to achieve this end, and consequently Byzantine behaviour often appeared devious and even duplicitous to outsiders. This was made worse by the weakened Empire’s need for allies, including, where necessary, Muslim rulers such as Saladin. In fact the Byzantine Empire’s greatest strength was now diplomatic rather than military. The Byzantines feared the Holy Roman Empire in particular, and so they cultivated good relations with Pisa, Genoa, the papacy and Venice. Unfortunately, Emperor Alexios III was unsympathetic to Venetian merchant communities within his own territory, and also overrated the power of the pope. When the crisis came, Pisan support was temporary while that of the Genoese was weakened by recent quarrels.
The result was a sort of paralysis, sometimes sticking to traditional diplomacy, sometimes trying to conciliate the western powers, sometimes doing nothing at all. Not that the Byzantine elite were unaware of the danger. The year before the Fourth Crusade set out, Emperor Alexios III reached a peace agreement with the revived Bulgarian state – previously considered rebels – under which the Byzantines retained lowland Thrace, the Rhodope mountains and Macedonia in return for recognizing Bulgarian independence.
Large numbers of Byzantine manuscripts were sent to Russia to be used in Orthodox Christian religious services, including this psalter dating from the 12th century. (State Public Library, Ms. Gr. 105, St Petersburg)
The fortifications defending the northern side of Constantinople faced the Golden Horn and so were not as strong as the landward walls facing west, these being in the Ayvansaray area. (Author’s photograph)
Since the Byzantine navy had decayed to a shadow of its former self, all that remained beyond a failing diplomacy were fortifications and garrisons. Strong modern fortifications had been erected around the Blachernae Palace in Constantinople only a few decades earlier, and here, unlike the more-famous but also more-archaic fortifications elsewhere in the Byzantine capital, the towers contained smaller chambers with small loopholes rather than large embrasures; perhaps this was to accommodate a new weapon, the crossbow. The towers themselves were also bulkier, probably to support new counterweight trebuchets. The Crusaders would also attack the fortifications along the Golden Horn, which, although considerably weaker than those facing the land, were fronted by open water.
Throughout much of Byzantine history the population of the imperial capital disliked having large numbers of troops within their city. As a result Constantinople was normally lightly defended, given its huge size. Furthermore, the cost of maintaining a substantial garrison was high, whereas threats remained rare. What’s more, the presence of large numbers of armed men was seen as a potential threat to the Emperor’s throne. Consequently, Byzantine rulers tended to prefer small, elite guard regiments such as the Varangians. When danger did arise, it was normal to assemble troops from neighbouring regions. However, the Fourth Crusade clearly caught the defenders of Constantinople on the wrong foot and there is little evidence of additional troops arriving from elsewhere.