This "debate" is about chapter 18 in the Quran... you can read about it here
وَيَسْأَلُونَكَ عَن ذِي الْقَرْنَيْنِ قُلْ سَأَتْلُو عَلَيْكُم مِّنْهُ ذِكْرًا {83}
[Pickthal 18:83] They will ask thee of Dhu'l-Qarneyn. Say: I shall recite unto you a remembrance of him.
إِنَّا مَكَّنَّا لَهُ فِي الْأَرْضِ وَآتَيْنَاهُ مِن كُلِّ شَيْءٍ سَبَبًا {84}
[Pickthal 18:84] Lo! We made him strong in the land and gave him unto every thing a road.
فَأَتْبَعَ سَبَبًا {85}
[Pickthal 18:85] And he followed a road
حَتَّى إِذَا بَلَغَ مَغْرِبَ الشَّمْسِ وَجَدَهَا تَغْرُبُ فِي عَيْنٍ حَمِئَةٍ وَوَجَدَ عِندَهَا قَوْمًا قُلْنَا يَا ذَا الْقَرْنَيْنِ إِمَّا أَن تُعَذِّبَ وَإِمَّا أَن تَتَّخِذَ فِيهِمْ حُسْنًا {86}
[Pickthal 18:86] Till, when he reached the setting-place of the sun, he found it setting in a muddy spring, and found a people thereabout. We said: O Dhu'l-Qarneyn! Either punish or show them kindness.
قَالَ أَمَّا مَن ظَلَمَ فَسَوْفَ نُعَذِّبُهُ ثُمَّ يُرَدُّ إِلَى رَبِّهِ فَيُعَذِّبُهُ عَذَابًا نُّكْرًا {87}
[Pickthal 18:87] He said: As for him who doeth wrong, we shall punish him, and then he will be brought back unto his Lord, Who will punish him with awful punishment!
وَأَمَّا مَنْ آمَنَ وَعَمِلَ صَالِحًا فَلَهُ جَزَاء الْحُسْنَى وَسَنَقُولُ لَهُ مِنْ أَمْرِنَا يُسْرًا {88}
[Pickthal 18:88] But as for him who believeth and doeth right, good will be his reward, and We shall speak unto him a mild command.
ثُمَّ أَتْبَعَ سَبَبًا {89}
[Pickthal 18:89] Then he followed a road
حَتَّى إِذَا بَلَغَ مَطْلِعَ الشَّمْسِ وَجَدَهَا تَطْلُعُ عَلَى قَوْمٍ لَّمْ نَجْعَل لَّهُم مِّن دُونِهَا سِتْرًا {90}
[Pickthal 18:90] Till, when he reached the rising-place of the sun, he found it rising on a people for whom We had appointed no shelter therefrom.
كَذَلِكَ وَقَدْ أَحَطْنَا بِمَا لَدَيْهِ خُبْرًا {91}
[Pickthal 18:91] So (it was). And We knew all concerning him.
ثُمَّ أَتْبَعَ سَبَبًا {92}
[Pickthal 18:92] Then he followed a road
حَتَّى إِذَا بَلَغَ بَيْنَ السَّدَّيْنِ وَجَدَ مِن دُونِهِمَا قَوْمًا لَّا يَكَادُونَ يَفْقَهُونَ قَوْلًا {93}
[Pickthal 18:93] Till, when he came between the two mountains, he found upon their hither side a folk that scarce could understand a saying.
قَالُوا يَا ذَا الْقَرْنَيْنِ إِنَّ يَأْجُوجَ وَمَأْجُوجَ مُفْسِدُونَ فِي الْأَرْضِ فَهَلْ نَجْعَلُ لَكَ خَرْجًا عَلَى أَن تَجْعَلَ بَيْنَنَا وَبَيْنَهُمْ سَدًّا {94}
[Pickthal 18:94] They said: O Dhu'l-Qarneyn! Lo! Gog and Magog are spoiling the land. So may we pay thee tribute on condition that thou set a barrier between us and them?
قَالَ مَا مَكَّنِّي فِيهِ رَبِّي خَيْرٌ فَأَعِينُونِي بِقُوَّةٍ أَجْعَلْ بَيْنَكُمْ وَبَيْنَهُمْ رَدْمًا {95}
[Pickthal 18:95] He said: That wherein my Lord hath established me is better (than your tribute). Do but help me with strength (of men), I will set between you and them a bank.
آتُونِي زُبَرَ الْحَدِيدِ حَتَّى إِذَا سَاوَى بَيْنَ الصَّدَفَيْنِ قَالَ انفُخُوا حَتَّى إِذَا جَعَلَهُ نَارًا قَالَ آتُونِي أُفْرِغْ عَلَيْهِ قِطْرًا {96}
[Pickthal 18:96] Give me pieces of iron - till, when he had levelled up (the gap) between the cliffs, he said: Blow! - till, when he had made it a fire, he said: Bring me molten copper to pour thereon.
فَمَا اسْطَاعُوا أَن يَظْهَرُوهُ وَمَا اسْتَطَاعُوا لَهُ نَقْبًا {97}
[Pickthal 18:97] And (Gog and Magog) were not able to surmount, nor could they pierce (it).
قَالَ هَذَا رَحْمَةٌ مِّن رَّبِّي فَإِذَا جَاء وَعْدُ رَبِّي جَعَلَهُ دَكَّاء وَكَانَ وَعْدُ رَبِّي حَقًّا {98}
[Pickthal 18:98] He said: This is a mercy from my Lord; but when the promise of my Lord cometh to pass, He will lay it low, for the promise of my Lord is true.
وَتَرَكْنَا بَعْضَهُمْ يَوْمَئِذٍ يَمُوجُ فِي بَعْضٍ وَنُفِخَ فِي الصُّورِ فَجَمَعْنَاهُمْ جَمْعًا {99}
[Pickthal 18:99] And on that day we shall let some of them surge against others, and the Trumpet will be blown. Then We shall gather them together in one gathering.
From the above you can deduce that a man named Zho El-Qarnyen ( of two horns) created a dam of iron to trap (Gog, and Magog) in until such a time when Allah should will them to be freed as one of the signs of the end-- the argument is about Zho _el -Qarnyen's identity-- some believe he is Alex the great... but many know that it couldn't have been... we may never know who he was some of us (me) believe it was prophet Solomon-- it is really inconsequential at this stage.. he was a righteous man ( Alex-- wasn't a righteous man-- nor a man of G-D)
We don't revere Alex the great from an Islamic point of view.. though there is no denying he was an important historical figure no more important than ghengis khan...
peace!