The Qureshite community had one important dream: The destruction of Mohammed and his religion. Pagan tribes outside Mecca were sharing with them the same dream. Like the Meccans, these tribes considered Mohammed a serious menace to their religion. This belief brought these tribes and the Muslims into military confrontations in which the Muslims had the upper hand. These tribes, therefore, were like the Meccan community full of resentment and rancor towards Mohammed and his religion.
There were clashes between the Muslims and some of the people of scripture who were neighboring Medina caused by their breaching of covenants with the Holy Prophet. Tribes from among them such as Banu Al-Natheer and others were exiled by the Prophet.
A delegation from these people went to Mecca and other Arab communities during the fifth year after the Hijrah, propagating war against the Prophet and attempting to mobilize the Arab forces for the proposed war. They did not need much effort to persuade the Meccans to a military undertaking against the Prophet. Their response to the invitation was prompt, and without hesitation, they mobilized four thousand fighters. This army was supplemented with six thousands from Ghatafan, Saleem, and other tribes. Thus, ten thousands strong marched towards Medina.
The Holy Prophet received the news of the imminent invasion a few days before their arrival at Medina. He consulted his companions, and Salman Al-Farisi (the Persian) advised the Prophet to dig a moat around Medina to prevent the invaders from entering it. The Messenger commanded the Muslims (who were about three thousands) to implement the plan. The moat was dug within six days.
Witnessing the moat, the invaders were surprised and realized that it had become difficult for them to enter Medina. Thus they found it necessary to besiege Medina instead of invading it directly. Banu Quraidhah, a community from the followers of the Scripture, joined the pagan army after its arrival. This community had a covenant of peace with the Prophet. Their treacherous action was a frightening surprise to the Muslims. By breaching the covenant, this community gave the pagan army additional forces and equipment. It became the duty of the Muslims to add to their defensive lines another line.

The Muslims in horror
There were many hypocrites among the Muslims who circulated frightening rumors, which added to the fear of the Muslims. The Holy Qur'an tells us of the psychological crisis with which the Muslims lived during that period:
"Behold! They came upon you from above you and from below you, and when the eyes grew wild and the hearts gaped up to the throats, and ye imagined various (vain) thoughts about God! In that situation the believers were tried: They were shaken with a mighty Shock. And behold! The hypocrites and those in whose hearts there is disease (even) say: God and His Apostle promised us nothing but delusion! Behold! A party among them said: O people of Yathrib (Medina), you cannot stand (the attack), therefore turn back! And a band of them ask for leave of the Prophet, saying: Truly our houses are bare and exposed though they were not exposed; they intended nothing but to flee." (33:10-13)
The pagan army, on the contrary, was enjoying an extremely high morale. Victory to them was certain. Medina was under their siege, and its inhabitants did not possess the courage to come out of it. Their confidence in victory and morale went higher when Banu Quraidhah joined them. This made them change their strategy from the siege of Medina to a direct invasion.

Amr's Venture
Amr Ibn Abd Wodd, accompanied by Dhirar Ibn Al-Khattab, Akramah Ibn Abu Jahl, and others, sought and found a narrow place in the moat. Their horses leaped above the moat to the other side. Had this adventure succeeded many pagan fighters were expected to follow them and make it feasible for the whole army to pass through that narrow place, for they could have spanned the two sides of the ditch by filling that narrow gap with soil.
The Muslims were in a state of shock and horror before the passage of these pagan soldiers to their side. The new danger, which was presented by their passage, made the morale of the Muslims much lower than before.

Men of strong faith
Though the hearts of most of the Muslims were filled with fear, some of them were unshaken by the new danger. It rather made their faith stronger in God, His Messenger, and the promised victory. These individuals were ready to sacrifice themselves and one of them certainly was determined to try to confine the danger, then to remove it. The Holy Qur'an tells us of the morale of these believers.
When the believers saw the confederate forces, they said: This is what God and His Apostle had promised us. And God and His Apostle told us what is true. And it only added to their faith and their zeal in obedience. "Among the believers are men who have been true to their covenant with God: Of them some have completed their vow (to the extreme), and some (still) wait; but they have never changed (their determination) in the least." (33:23)
The Holy Qur'an does not inform us of the number of those believers whose faith was increased by the increase of the danger. These believers may have been scores or just a few. However, faith sometimes remains only as a state of mind without being transformed into action. Some of the faith is active, flowing with vitality and moving the faithful to face the danger and to rise to its level and above its level.
The number of these distinguished believers remained unknown.

Ali's Response
However, history informed us of one of them because of his outstanding achievements at this battle, in confining and removing the danger, which shook the very foundation of the Islamic state. That man was no other than Ali Ibn Abu Talib.
Amr Ibn Wodd, who crossed the moat, was well known among the Arabs. He attended the battle, boastfully making his place known to people. His very passage from one side to the other side of the moat, accompanied only by a small number of fighters, indicates that the man was extremely courageous. He was the only one from among the ten thousand fighters who tried to invade the Muslims directly and challenge them totally while he was with them on one side.
The passage of Amr and his companions presented to the Muslims a new and serious danger and a frightening surprise, which they never expected. The door was about to be opened widely, and hundreds and thousands were expected to follow. The surprise, however, did not frighten or astonish Ali. History informs us of Ali's present-mindedness and fast response, for he immediately moved to confine the danger, then to remove it. Leading a small number of believers, he went immediately to the point where the Islamic defense line was broken by the passage of Amr. He had his companions stand there, preventing others from attempting to follow Amr. And after he confined the new danger, he managed to remove it completely.
While mounting his horse, Amr went around the area of Sal'a, facing the Muslims and challenging them: "Is there any dueler?" He repeated this call but there was no response on the part of the companions. This compelled Ali to leave his place where he was deterring the pagan forces from following Amr by crossing the Moat. Responding to Amr's challenge, he left that place temporarily to be defended by the few who were with him.
He neared Amr and asked him to face him in a duel. At this moment the Prophet (S.A.W.) uttered this historical sentence: "Entire faith is facing entire infidelity". Amr arrogantly replied: "Why, son of my brother (Amr was a friend of Abu Talib, father of Ali)? By God, I would not like to kill you." Ali replied: "But, by God; I would love to kill you." A short but extremely violent duel between the two heroes took place. Ali killed Amr immediately and Amr's companions ran away, trying to re-cross the moat from the Islamic side to the pagan side.
Ali exclaimed: "Allahu Akbar," (God is Great) and so did the Muslims. The death of Amr was the end of the new danger. Those who were with him ran away, trying to save their skin; but most of them were killed before they could cross to the other side.
Ali made a great contribution in the defense of Islam at this battle during which the danger against the new Faith reached its peak.
At this battle the Muslims faced a greater danger than ever before. The elements of the Islamic defense were the same three elements which played their roles during the two battles of Badr and Ohod: The firmness of the Messenger and his ideal leadership: the heroism of Ali; and the determination of the Islamic army.
A fourth element was added at this battle: The role of Salman Al-Farisi (the Persian) who counseled the Prophet to dig the moat around Medina.
The role of the Islamic army during the Battle of Ohod was smaller than its role during the Battle of Badr. And it was less important at the Battle of the Moat than it was at the Battle of Ohod, for the Muslims during the Battle of the Moat did not even dare face the enemy. They only dug the moat around the city before the arrival of the pagan army then stood behind the moat until the end of the battle.
The roles of the first two defensive elements were similar to their roles at Badr and Ohod and probably bigger. The firmness of the Messenger, his leadership, his war strategy and his speed in digging the moat were most essential in making the Muslims pass the crisis safely.
Ali's role at this battle was outstanding in the history of the Islamic defense.

The magnitude of Ali's contribution
It would not be logical to say that the Muslims were unable collectively to kill Amr, who could not by himself prevail against thousands of Muslims. But this was not the case. Amr was calling for a duel. A duel could only be between two persons. It was considered to be shameful for two men or more to have a duel with one man. Amr challenged all the Muslims to send one of them to have a duel with him. None of them was willing to face him except Ali.
Nor would it be logical to say that Amr was the entire power of the pagan forces, and that his death was a defeat for the whole confederate army. But it would be logical to affirm two important matters:
1. Ali's initiative to block the passage point and prevent others from following Amr had stopped the danger and confined it. Had the passage point remained open, a great number of the pagan soldiers would have followed Amr and their passage could have resulted in establishing a bridge between the two sides of the moat. Such a bridge would enable the whole army to cross.
One hour of negligence could have led to a decisive defeat of the Islamic army. This did not happen because Ali was fast in his response to the new danger, present minded, calm and collective and ready to deal with the serious crisis.
2. The death of Amr proved to the pagan army that they were unable to pass the moat again, and that what Amr could not accomplish could not be accomplished by others. By this the pagan army had to face one of two alternatives: Withdrawal, or continuation of the siege until the Muslims surrender or were forced to cross the moat and fight the pagans. The continuity of the siege of Medina was beyond the ability of the pagan army. It did not have the food supplies for ten thousand fighters and their horses and camels, which could enable them to continue the siege for several months or weeks. In addition, a hurricane like wind went on causing the pagan army many damages and making its life miserable. The hurricane was preceded by an argument between the pagans and their Jewish allies, which made their co-operation in the battle highly difficult.
Thus, there was only one alternative for the pagan army to take after the failure of Amr and his death: The withdrawal and that is what they did.
We ought not to forget an important matter! The death of Amr and most of his companions raised the morale of the Muslims. Their hope in continuity of life and in victory was revived. All this was a result of Ali's endeavor, and by this we can understand the meaning of the declaration of the Prophet: "The duel of Ali Ibn Abu Talib against Amr Ibn Abd Wodd at the Battle of the Moat out weighs the good deeds of my whole nation until the Day of Judgment."
The Confederate Army withdrew and the Muslims passed the crisis safely. They regained their confidence concerning the future because of failure of the Confederate forces after their biggest mobilization. The Messenger said after their withdrawal: "After today, we shall invade them and they will not invade us."