The emergence of Christianity during the height of the Roman Era became a problem for the Romans. The more the Roman government tried to suppress Christianity the more Christianity grew. Since they couldn't eliminate Christianity they decided to merge their belief system with it.
The moral decline of the Church can be traced back to the aforementioned Emperor Constantine. The beliefs of the Babylonians, Egyptians, Greeks, Eastern cultures, and Romans infiltrated Christianity as the Roman government merged with Christianity. At the heart of the infiltration was Gnosticism which means salvation through knowledge. Christianity, of course, is salvation through Christ.
Fast forwarding we see a military and religious order emerge out of Jerusalem in 1118 known as the Knights Templar. By 1128 the group was given special protection from the Pope. Comprised of mostly nobility the Knights Templar were granted many favors from European rulers. They became wealthy through gifts of land and money. Pope Clemente V resisted abolishment of the Knights Templar for years but was persuaded by the public and King Phillipe IV of France to have 54 knights burned alive in Paris as punishment for "conspiracy and Satan worship (notably Baphomet worship which is prevalent in Hollywood today) The remaining members of the order fled to Scotland, Portugal, and the Island of Malta. Today's well connected youth (notably former President Bill Clinton among others) are initiated in to the Order of DeMolay a secret society which is derived from the Knights Templar.
The Rosicrucians were a religious order that combined the beliefs of ancient mystery religions with Christianity. At some point this group merged with the Knights Templar. After the Knights Templar were abolished, the Rosicrucians became the vehicle by which occult teachings were spread throughout Europe. Freemasonry started when the Rosicrucians merged with the Stone Mason Guilds of Europe. From the 1640's and onward as the construction of Grand Cathedrals declined, Masons concentrated less on stone work and more on occult teachings. By 1717 the worlds first grand lodge of freemasonry was established in London. Freemason were initially viewed positively by the public and were known for doing good works. The number of lodges grew rapidly throughout Europe. The age old Satanic (Luciferian) desire for power also grew within Freemasonry. A secret society within a secret society know as the Illuminati was born on May 1st, 1776. Their goals were quite clear:
Abolition of all monarchial government and patriotism to it.
Elimination of private property and inheritance.
Destruction of the traditional family.
Eradication of all religion.
The perversion of the Catholic Church and the modern day Pope with his Vatican Mafia is well do ented as I digress.