How did christianity kill the roman religion?

I was pondering upon this issue after reading a few articles about the downfall of the Roman religion... How did Christianity succeed to take the place of the Roman religion in such a short time? One hypothesis historians have brought forward was that, as the Roman Empire began to crumble, the empire switched to Christianity to help stabilize it. There is one mentioning of the Roman historian Pliny the Younger that Jesus' life and the miracle of the resurrection was so convincing that some of the Romans gave up their gods immediately.

It seems pretty curious to me that people would just give up a millennium-old religion in a matter of decades...

Maybe it was partly because Christianity promised more than the Pagan faiths. It had a God who could not screw-up like Zeus, and it promised eternal life in a blissful place to believers. Of course, I may be way off base, as I don't know very much about ancient paganism as a religion.

There were many reasons for this.
RLynn touched on some of them.
Christianity made it easy for anyone to join, and it promised so much.
Some have said that if Christianity never showed up, Mithraism might have been the dominant religion.
But this faith was open only to men.
Also, many religions required an initiation; They were costly and exclusive "clubs".
Christianity just required baptism, and it was open to the lowliest of the low.
Check out Walter Burkert's Ancient Mystery Cults.

What Joe said. (I forgot about the mystery cults.) Christianity incorporated some of the themes of the mystery religions, which made it a tad easier for Pagans to swallow. The cult of Isis, lovingly described in Apuleius' The Golden Ass and the inspiration for Mozart's The Magic Flute, sounds like something I would enjoy joining.

Maybe it was partly because Christianity promised more than the Pagan faiths.

Yes, you have to admit the Christian heaven sounds a lot more appealing than the gray dullness of Hades. The idea of a powerful, protective father figure instead of a capricious, squabbling pantheon probably drew more in as well.

Am not really very familiar about this, but if what I read is true, it is said that when the Catholic Church was established, it adopted the pagan icons as religious icons, like Isis became Mother Mary, and the rituals and festivals were also adopted as Christian rituals and festivities.

This was largely true, especially when the Church began missionary work. I think it is strong evidence of the Pagan origins of Christianity. To me this enhances, rather than detracts from, the validity of the Christian mythos.

Nero also aided in the transaction, when people of Rome saw the Christians so fearlessly burn at the stake refusing to renounce their faith, other Romans started to believe it was a strong religion.

"Their martyrdom was a message. Many were amazed at the courage of these men and women. What must be in their faith which made them stand so fast? Soon there were more converts. Irenaeus, a bishop of Lyon (ancient Lugdunum) in the second century A.D, would one day say, "the blood of the martrs is the seed of the church" -Roman Redities

i think that the roman state made a lot of people powerless over their own lives.

one difference between pagans and christians is that pagans don't think of themselves as invincible. but christianity introduced the idea of invincibility of spirit.
by making so much of the population impotent the roman state created an environment where paganism couldn't thrive, and people took back their sense of power by believing in spirit.

you could say that the romans killed their own religion.

I would imagine that as the Roman Empire disintegrated, that not only faith in the government but faith in the Roman gods greatly diminished. Needing to believe in something, Christianity offered hope at a time when hope was in short supply.

It's hard for me to conceive of worshipping the Roman gods. They just really don't seem worthy of worship. Even simple veneration would be hard. I do, however, believe that they are psychologically important as personifications of components/aspects of the human psyche. (Of course, modern religions also can be tough to swallow, requiring mental gymnastics such as the voluntary suspension of one's critical faculties.)

I'm pretty sure that it all started with Constantine the Great, the Emperor of Rome. He was the first Christian emperor of Rome and it was because of him that Rome was unified and all other would-be emperors were dispatched.
Just before a great battle against Maxentius, a wanna-be emperor, Constantine was visited by Christ in a dream. He painted Christ's symbol on the shields of all of his men, which were four times less than that of Maxentius', before battle. Constantine and his men defeated Maxentius' men and, as they were fleeing over a bridge, it collapsed and Maxentius and all of his thousands of troops were drowned. Constantine believed that his victory was entirely attributed to Christ and so named himself the Emperor of the Christian people.
For some time after this Christians were rarely persecuted. Emperor Constantine still allowed Pagans their gods especially the sun god whose face or name, I believe, is on one of his coins. Property was returned to Christians and they were, once again, allowed to purchase land and worship openly.
As time went on Constantine became more involved with the Christian church. He sought to resolve theological disputes among the church.
In this role he summoned the bishops of the western provinces to Arelate after the Donatist schism had split the church in Africa. He worked to solve debates peaceably but brutal enforcement of the decisions reached at such meetings was not uncommon. Following the decision of the council of bishops at Arelate, donatist churches were confiscated and the followers of this branch of Christianity were brutally repressed. Evidently Constantine was also capable of persecuting Christians, if they were deemed to be the 'wrong type of Christians'.
Licinius, Constantine's brother-in-law and emperor in the east, I believe, began to oppose him and persecute Christians again and even started ejecting them from their positions in the government. The two fought repeatedly. Finally Constantine defeated and later executed Licinius, becoming the sole ruler of Rome. Soon afterwards Pagan sacrifices were outlawed and money taken from Pagan temples was given to Christians to build churches. Gladiator sports were outlawed and Jews were no longer allowed to own Christian slaves.
He made some pretty severe laws and had pretty harsh taxes, but the people loved him, mostly because of the prosperity and peace he brought to Rome.
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And thus ends the debate
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We touched on this idea briefly in my first semester of Anthropology: Christianity was created for the poor and Catholocism was a religion for the rich. Constantly in the Bible you read about how very few rich people will make it into Heaven. It was easy for people to believe in a god that was protecting them and providing for them when they had nothing. They were able to take comfort in the idea that in the end "the last [would] be first and the first [would] be last". God even say that "it is easier for a camel to go through the eye of a needle than for a rich man to enter the kigdom of God".
While Catholics have lavish and expensive temples and robes and ceremonies, it would seem that Christians pride themselves on their simplicity, "come as you are".
Perhaps because the poor outnumbered the wealthy it was easy for Christianity to catch on after Constantine made it okay to practice openly.

Nadai, are you implying that Catholics are not Christians?

Indeed

Hmmmm...... Hard-core, industrial-strength Protestantism.

This is all entirely my opinion and hopefully won't be taken the wrong way by anyone. If it is, I apologize. I would never say that one religion is better than another, I learned how to avoid such things while studying Anthropology, and I know that each individual has their own ideas, not one greater than anothers; we all have our own opinions about the world and our place in the world, this is mine.
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Christianity is built solely on the Bible, God's Holy Law. It is the infallible rule of faith for Christians. The Bible alone contains anything and everything a Christian needs to live a holy and saved life before Him. Christianity stands on the Gospel of God's grace. God's son became man and gave His life as a ransom to secure the freedom of Christians who follow God's Word from sin. God graciously grants His people repentance through Him if they trust in Him and admit His sacrifice and that He went to the cross and rose from the grave for our salvation. Believers are accepted by Christ, solely on the merit of His righteousness and blood-sacrifice, not because of any past good or bad deeds. God then sends His Holy Spirit to dwell inside His people so that they can inherit the Kingdom of Heaven.

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Roman Catholocism requires submission of ones self to doctrines taught by the Roman magisterium i.e. the Pope and bishops. Catholics derive their doctrines Scriptures and Sacred Tradition (which can only be known through the magesterium) but Catholics aren't even given access to the original sources because they are only seen by the magisterium who establishes their authentic meaning. The Bible is open for anyone and everyone who would like to read it, Christian or not; how a person interprits what they read is entirely between them and God. Roman Catholicism means (in my opinion) slavery to the Vatican. For Catholics, forgiveness can only be obtained through the sacrament of penance. The benefits of Christ's sacrifice are accessible through the sacrifice of the Mass. Instead of teaching the faithful to rest in Christ by faith, Catholics are taught to perform religious works to "merit grace" and to do penance to make satisfaction. Even after death, Catholics remains dependent on the "Church" to relieve their suffering in Purgatory by masses and indulgences.

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So do I think they're the same... no. If Catholics were Christians they'd call themselves Christians not Catholics. There are several types of Christians, but they all have the privelage of calling themselves thus. Protestantism may be considered by some to be a type of Christianity, fair enough. Some religions and some people who practice religion believe that, because they say they're Christian or acknowledge that there is a god that they are Christian, they would be sorely mistaken.
Am I a Protestant...I like to think of myself as a nondenominational Christian, but if I am I'd think I were more liberal than "hard-core, industrial-strenght", but then I suppose that any religion for some is too much.

I suppose this thread is getting dangerously off topic, but I should like to respond to your final paragraph. You have created a semantical issue regarding the term Chriatian. All Catholics consider themselves Christian, as do adherents of the Greek Orthodox, Baptist, Methodist, Episcopal, Presbyterian, Nondenominational, and many other persuations. Yet you wish to restrict the term Christian to those who adhere to a particular version of Pauline theology. Were there no true Christians before Saul of Tarsus had his famous epileptic fit on the road to Damascus and thereafter formulated his theology and enlightened the world on the 'true' meaning of the Christ-event? I should think that the concept of salvation by grace through faith (i.e., Christianity) would not be so exclusive. But what do I know?