Romanesque is a term that was started by art historians in the 1800’s. The term refers to the art of Western Europe from about 1000 AD to around the 13th century which was when Gothic styles started to become more used. Romanesque Styles, just to name a few include: The barrel vaults which is a type of vaulted roof in which a single arched surface extends from wall to wall. Another style is the Groin vault which mostly square in plan and is constructed of two barrel vaults intersecting at right angles.
To understand why these building were so extravagant you first must understand the time period they were made in. This period came shortly after the turn of a new millennium and people were rejoicing in the fact that they were still alive. At this point in time people thought the world was going to end in the year 1000. This obviously would prove not to be true, but the celebration the people would have felt could have had great influence in the building of extravagant churches. It is almost like they were thanking God for letting them live. You can imagine this felling of rejoice since about 10 years ago we went through the same thing while bringing in the year 2000 people though the world was going to end then as well.
So if you take the superstitious mindset that existed back then add the fact that the majority of the population believed the earth’s impending doom was predetermined. It would not be too hard to understand why they would want to build these extravagant structures. Perhaps they felt like they were obligated to make these sacrifices of money and time to give thanks to the lord. The big difference between the bring in of the year 2000 and the bringing in or the year 1000 is that knowledge is better distributed now days and there is a lot more to do than build huge buildings.