I believe that a marriage, in its most basic sense, is a promise that two people make to each other -- a covenant. A very important covenant.
So really, witnesses come in because witnesses are necessary things generally speaking for an important covenant, or else no one can prove that it actually happened, that one of them did not lie and say that the other consented to the covenant, and so on. They have witnesses for wills, for treaties, all the really important stuff, and considering that marrying someone is a really important promise, you would have to have witnesses, so that if someone challenges the validity, or claims that one of the two are breaking the covenant, they have proof that the covenant exists. (Oh, and when it comes to the number of witnesses to adequately prove the marriage, I would say the more the better (to a point of course 0.0), but with a minimum of two, based off of the minimum for condemning someone to death.)
As for anything else that generally pertains to marriage -- rituals, customs, and so on -- in my opinion it is purely symbolic or habitual.
You would still be married without any of it, just as you would still be saved even if you could never get baptized (like the thief on the cross).When it comes to legality, and whether a marriage is a marriage even if they don't go through all the hoops that the state says are mandatory, again, I look at it like a covenant -- a contract -- an agreement. The government wants the records for all that stuff, because otherwise they can't enforce a contract when someone tries to break it. But it would still be a marriage, even if you deny the government that information and they won't respect what you have as proof. It would just be really difficult to survive in our highly governmentalized world. * bleak face *
Batman wrote:
In some Native American cultures, the man took his fiancee into the wilderness for a certain amount of time, and when they returned, they were considered man and wife.
There isn't much detail in that statement, but I would say that if they promised to marry each other at some point, then that would be a marriage, and if they had witnesses that they promised, then that would be a provable marriage. They had better promise before they go out into wilderness together, though, because otherwise I would assume that they would be living like they were married while they were out there and that would be fornication.When it comes to whether you can have a marriage without parental consent, it, again, falls under the category of whether you can make a contract without parental consent.
Numbers 30: 3 - 5
3 If a woman also vow a vow unto the LORD, and bind herself by a bond, [being] in her father's house in her youth;
4 And her father hear her vow, and her bond wherewith she hath bound her soul, and her father shall hold his peace at her: then all her vows shall stand, and every bond wherewith she hath bound her soul shall stand.
5 But if her father disallow her in the day that he heareth; not any of her vows, or of her bonds wherewith she hath bound her soul, shall stand: and the LORD shall forgive her, because her father disallowed her.
So...basically you would have to decide what is meant by 'youth' here.
But regardless, you couldn't get married without your father's consent if you are seven years old. 
(Just as a proposition on the definition of 'youth', the Hebrew word means basically just that: 'properly, passive participle from 5288 as denominative; (only in plural collectively or emphatic form) youth, the state (juvenility) or the persons (young people): -- childhood, youth.' And as time and time again the Bible mentions all men, able to bear arms, and then defines that as 'twenty years old and upward', I would propose that when you turn twenty you are a man or woman rather than a youth.) (I am not proposing that when you turn twenty you should stop listening to your parents. 0.0)
When it comes to portraying it in your writing, I like to sometimes strip it really bare -- throw off all the finery that usually attends it. I like to point out that a marriage is a promise. Nothing more, nothing less.
I generally do this by having my characters get married in less than romantic circumstances sometimes...poor things 
...like while in hiding from a murderous and vengeful creed.
