When begin to look at sources outside fo the Quran, at secular scholars reports on the subject, you wil find that the crucifiction of Jesus of Nazareth is considered a historical fact.
Here's an article detailing evidence that the Romans did indeed crucify individuals: FRONTLINE: from jesus to christ: jesus many faces: crucifixion | PBS
Here's Wikipedia's article on the crucifiction which also presents jewish (Josephus and the Baylonian Talmud)and Roman(Tacitus) Roman sources. Crucifixion of Jesus - Wikipedia, the free encyclopedia
If you're not satisfied with these articles on their own, check the references they used for yourself. I would also recommend reading Lee Strobel's book, "The Case for Christ," which recounts his journey from atheist to born again Christian which resulted from his examination of the historical evidence for the divinity of Jesus of Nazareth. hwile some have considered his book somewhat one sided, he sites actual historical sources that anyone can investigate. If you're going to do honest research, you have to research all sources. I think you will be suprised at what you find.