France was one of the strongest states in Europe at the time, as the Albigensian Crusade had brought Provence into Parisian control.
Poitou was ruled by Louis IX's brother Alphonse of Poitiers, who joined him on his crusade in 1245.
Another brother, Charles I of Anjou, also joined Louis.
For the next three years Louis collected an ecclesiastical tenth (mostly from church tithes), and in 1248 he and his approximately 15,000-strong army that included 3,000 knights, and 5,000 crossbowmen sailed on 36 ships from the ports of Aigues-Mortes, which had been specifically built to prepare for the crusade, and Marseille.
Louis IX's financial preparations for this expedition were comparatively well organized, and he was able to raise approximately 1,500,000 livres tournois.
However, many nobles who joined Louis on the expedition had to borrow money from the royal treasury, and the crusade turned out to be very expensive.

They sailed first to Cyprus and spent the winter on the island, negotiating with various other powers in the east.
 The Latin Empire, set up after the Fourth Crusade, asked for his help against the Byzantine, Empire of Nicaea, and the Principality of Antioch, and the Knights Templar wanted his help in Syria where the Muslims had recently captured Sidon.

Nonetheless, Egypt was the object of his crusade, and he landed in 1249 at Damietta on the Nile.
Egypt would, Louis thought, provide a base from which to attack Jerusalem, and its wealth and supply of grain would keep the crusaders fed and equipped.

On 6 June Damietta was taken with little resistance from the Egyptians, who withdrew further up the Nile.
 The flooding of the Nile had not been taken into account, however, and it soon grounded Louis and his army at Damietta for six months, where the knights sat back and enjoyed the spoils of war.
Louis ignored the agreement made during the Fifth Crusade that Damietta should be given to the Kingdom of Jerusalem, now a rump state in Acre, but he did set up an archbishopric there (under the authority of the Latin Patriarch of Jerusalem) and used the city as a base to direct military operations against the Muslims of Syria.

In November, Louis marched towards Cairo, and almost at the same time, the Ayyubid sultan of Egypt, as-Salih Ayyub, died.
A force led by Robert of Artois, alongside the Templars and the English contingent led by William Longespée, attacked the Egyptian camp at Gideila and advanced to Al Mansurah where they were defeated at the Battle of Al Mansurah.
Robert and William were killed, and only a small handful survived.
Meanwhile, Louis' main force was attacked by the Mameluk Baibars, the commander of the army and a future sultan himself.
Louis was defeated as well, but he did not withdraw to Damietta for months, preferring to besiege Mansourah, which ended in starvation and death for the crusaders.
In showing utter agony, a Templar knight lamented:
Rage and sorrow are seated in my heart ... so firmly that I scarce dare to stay alive.
 It seems that God wishes to support the Turks to our loss ... ah, lord God ... alas, the realm of the East has lost so much that it will never be able to rise up again.
They will make a Mosque of Holy Mary's convent, and since the theft pleases her Son, who should weep at this, we are forced to comply as well ... Anyone who wishes to fight the Turks is mad, for Jesus Christ does not fight them any more.
 They have conquered, they will conquer.
 For every day they drive us down, knowing that God, who was awake, sleeps now, and Muhammad waxes powerful.

In March 1250 Louis finally tried to return to Damietta, but he was taken captive at the Battle of Fariskur, where his army was annihilated.
Louis fell ill with dysentery, and was cured by an Arab physician.
In May he was ransomed for 800,000 bezants, half of which was to be paid before the King left Egypt, with Damietta also being surrendered as a term in the agreement.
 Upon this, he immediately left Egypt for Acre, one of few remaining crusader possessions in Syria.
France was one of the strongest states in Europe at the time, as the Albigensian Crusade had brought Provence into Parisian control. Poitou was ruled by Louis IX's brother Alphonse of Poitiers, who joined him on his crusade in 1245. Another brother, Charles I of Anjou, also joined Louis. For the next three years Louis collected an ecclesiastical tenth (mostly from church tithes), and in 1248 he and his approximately 15,000-strong army that included 3,000 knights, and 5,000 crossbowmen sailed on 36 ships from the ports of Aigues-Mortes, which had been specifically built to prepare for the crusade, and Marseille. Louis IX's financial preparations for this expedition were comparatively well organized, and he was able to raise approximately 1,500,000 livres tournois. However, many nobles who joined Louis on the expedition had to borrow money from the royal treasury, and the crusade turned out to be very expensive.
They sailed first to Cyprus and spent the winter on the island, negotiating with various other powers in the east.  The Latin Empire, set up after the Fourth Crusade, asked for his help against the Byzantine, Empire of Nicaea, and the Principality of Antioch, and the Knights Templar wanted his help in Syria where the Muslims had recently captured Sidon.
Nonetheless, Egypt was the object of his crusade, and he landed in 1249 at Damietta on the Nile. Egypt would, Louis thought, provide a base from which to attack Jerusalem, and its wealth and supply of grain would keep the crusaders fed and equipped.
On 6 June Damietta was taken with little resistance from the Egyptians, who withdrew further up the Nile.  The flooding of the Nile had not been taken into account, however, and it soon grounded Louis and his army at Damietta for six months, where the knights sat back and enjoyed the spoils of war. Louis ignored the agreement made during the Fifth Crusade that Damietta should be given to the Kingdom of Jerusalem, now a rump state in Acre, but he did set up an archbishopric there (under the authority of the Latin Patriarch of Jerusalem) and used the city as a base to direct military operations against the Muslims of Syria. 
In November, Louis marched towards Cairo, and almost at the same time, the Ayyubid sultan of Egypt, as-Salih Ayyub, died. A force led by Robert of Artois, alongside the Templars and the English contingent led by William Longespée, attacked the Egyptian camp at Gideila and advanced to Al Mansurah where they were defeated at the Battle of Al Mansurah. Robert and William were killed, and only a small handful survived. Meanwhile, Louis' main force was attacked by the Mameluk Baibars, the commander of the army and a future sultan himself. Louis was defeated as well, but he did not withdraw to Damietta for months, preferring to besiege Mansourah, which ended in starvation and death for the crusaders. In showing utter agony, a Templar knight lamented:
Rage and sorrow are seated in my heart ... so firmly that I scarce dare to stay alive.  It seems that God wishes to support the Turks to our loss ... ah, lord God ... alas, the realm of the East has lost so much that it will never be able to rise up again. They will make a Mosque of Holy Mary's convent, and since the theft pleases her Son, who should weep at this, we are forced to comply as well ... Anyone who wishes to fight the Turks is mad, for Jesus Christ does not fight them any more.  They have conquered, they will conquer.  For every day they drive us down, knowing that God, who was awake, sleeps now, and Muhammad waxes powerful.
In March 1250 Louis finally tried to return to Damietta, but he was taken captive at the Battle of Fariskur, where his army was annihilated. Louis fell ill with dysentery, and was cured by an Arab physician. In May he was ransomed for 800,000 bezants, half of which was to be paid before the King left Egypt, with Damietta also being surrendered as a term in the agreement.  Upon this, he immediately left Egypt for Acre, one of few remaining crusader possessions in Syria.
Seventh Crusade