Chapter 43: How the Pilgrims took the seashore of Constantinople [after 5th july 1203]
… And when the knights were returned from chasing the Greeks they spoke together, and the Venetians said that their vessels were by no means in safety unless they were inside the harbour. And they took counsel how to get them within the harbour. Now the harbour of Constantinople was firmly closed with a very thick chain, which was made fast on the one side within the city and on the other to the Tower of Galata. This tower was very strong and right easy to defend, and it was right well garrisoned with defenders.
Chapter 44: How the Tower of Galata was taken; and of the beginnings of the assault upon the city
By the advice of the notable men, this tower was invested, and at last it was taken by storm; but from end to end of the chain were galleys of the Grecians who were helping to defend the chain. But when the tower was taken and the chain broken, then did the vessels enter within the harbour and were brought into safety; and they took the galleys from the Greeks who were within the harbour, and certain ships also. And when their own ships and all their other vessels were brought inside the harbour in safety, then the pilgrims and the Venetians came together and took counsel amongst themselves how they might besiege the city. And at last they agreed between them that the Franks should invest the city by land, and the Venetians by sea. And the Doge of Venice said that he would cause engines to be built upon his ships, and ladders wherewith they could attack the walls. Then they armed themselves, the knights and all the other pilgrims, and went on to pass over a bridge which lay some two leagues away; nor was there any other road whereby to go to Constantinople within less than four leagues of that place, save only this bridge. And when they came to the bridge, certain Greeks came thither who disputed the passage as long as they could, until at last the pilgrims drove them back by force of arms and so passed over. …
Robert de Clari, The Fall of Constantinople, ch. 43, 44 [english translation online in: http://www.deremilitari.org/resources/sources/clari.htm]
The Fourth Crusade and The Conquest of Constantinople
… The Greeks made a goodly show of resistance; but when it came to the lowering of the lances, they turned their backs, and went away flying, and abandoned the shore. And be it known to you that never was port more proudly taken. Then began the mariners to open the ports of the transports, and let down the bridges, and take out the horses; and the knights began to mount, and they began to marshal the divisions of the host in due order.
Capture of the Tower of Galata
Count Baldwin of Flanders and Hainault, with the advanced guard, rode forward, and the other divisions of the host after him, each in due order of march; and they came to where the Emperor Alexius had been encamped. But he had turned back towards Constantinople, and left his tents and pavilions standing. And there our people had much spoil.
Our barons were minded to encamp by the port before the tower of Galata, where the chain was fixed that closed the port of Constantinople. And be it known to you, that any one must perforce pass that chain before he could enter into the port. Well did our barons then perceive that if they did not take the tower, and break the chain, they were but as dead men, and in very evil case. So they lodged that night before the tower, and in the Jewry that is called Stenon, where there was a good city, and very rich.
Well did they keep guard during the night; and on the morrow, at the hour of tierce, those who were in the tower of Galata made a sortie, and those who were in Constantinople came to their help in barges; and our people ran to arms. There came first to the onset James of Avesnes and his men on foot; and be it known to you that he was fiercely charged, and wounded by a lance in the face, and in peril of death. And one of his knights, whose name was Nicholas of Jenlain, gat to horse, and came to his lord's rescue, and succoured him right well, and so won great honour.
Then a cry was raised in the host, and our people ran together from all sides, and drove back the foe with great fury, so that many were slain and taken. And some of them did not go back to the tower, but ran to the barges by which they had come, and there many were drowned, and some escaped.
As to those who went back to the tower, the men of our host pressed them so hard that they could not shut the gate. Then a terrible fight began again at the gate, and our people took it by force, and made prisoners of all those in the tower. Many were there killed and taken.
Geoffroi de Villehardouin, Memoirs or Chronicle of The Fourth Crusade and The Conquest of Constantinople [english translation online in the Medieval Sourcebook: http://www.fordham.edu/halsall/basis/villehardouin.html]