"Firstly, Rome was a late civilization. Marriage existed well before roman matrimonium, it existed in Egypt, Messopotamia, India, wherever."
Yes, but they do not form the foundation of the currently known Western marriage, on which the marriage system of the West was founded. We recepted ROMAN marriage, not Messopotamian or other.
"Marriage was indeed meant to subdue women, the head of the family would always be the husband. Why do you think the term 'patriarchical society' is used?"
Because you do not know history, and because many historians refuse (outly) to look at the source instead of reading what other historians wrote and copy it. Patriarchal society comes from the pater familias who leads the family. Though, again, this is absolutely not as you think it would be.
The pater familias had better rights. Why? Because he 1. comes from a Roman couple that lived in matrimonium or 2. Because he had been in the army. The reason mostly men had civitatis (= could claim civil rights) was because women were not allowed in the army. A women could perfectly well start a family on her own, but it would not be as succesfull, for the women would proably be unable to claim civil rights. This changed around 167 B.C. though because then the system of fighting for your rights was altered and the main way of gaining civil rights was via matrimonium.
Now, why do I speak of a pater familias? Because a family came into existence around a person with civitatis. The family sought protection under it. They all wanted better rights as well, but since they could not (yet) get it, they sought to gain them via someone else. Look at the pater familias like a family lawyer, who protects those that are part of his family. Since a women could not offer that kind of protection (having no status civitatis till 167 B.C. when the system changes and it no longer matters that she can not be part of the military), female 'pater familias' were rather uncommon.
"The digests came very late in roman history."
It depends, the digests of Justinian which is what you refer to were created around 532 A.D. , but the are based on JURISPRUDENCE from Constantine (322 A.D.) etc. as well. Also, the Digests itsself refer to earlier sources (e.g. law of the XII tables), which means that the practice was common even then.
But since you are partially right, I also cited above the city laws of IRNI (called the Lex Irnitana), only discovered recently (around 1980 I believe), which dates back till around 100 A.D. These city laws are carved in stone, and next to every male 'demonstrative pronoun' (I'm not sure of this English translation) is written the female one. Proably because someone in court once tried to say that since all laws are written for 'males', they should not apply to protect females, and thus his client should go free.
"In fact, the roman family was even more patriarchical than barbarian families of the time (even Gaius admitted that)"
You are referring to text 55 of Gaius in the version of Ph. Meylan. I do not know if you are familiar with the text, but there are problems of translation there (as with any Latin text). "In potestate" is usually translated as absolute power, but it means being under the protection of the pater familias (as I explained at length above). This is normal for kids, for as minors they could not claim civil rights. The text also speaks of "Iustis nuptiis", which means legal wedding. It does not means matrimonium, or marriage. Thus, it's a bit confusing. But it is true that the Roman society was Patriarchal = with power to the pater familias, only the in potestate refers not to absolute power over the people in the family, but over the legal protection the people in the family recieved.
"Pater familias had all the power in his family"
Supra
"and his wife wouldn't even take over after his death - she'd fall under the potestas of the new pater familias"
All the goods of the decuius go to the ones of the blood, only in the Roman heritage system the longstliving husband could recieve something (though only in extremis, when all the other categories no longer could).
And that she falls under the protection of a new pater familias, that's only partially true. She could return under the protection of her father as a pater familias, or she could start a family herself. Only, then she wouldn't be as well protected (untill 167 B.C. that is). Also, she would be the beginning and the end of her family, since she cannot extent protection over other people. This means that the woman would form a family unto herself.
"Pater familias even had the right to sell his own children (wife?) to slavery - "trans tiberum"
Selling your children was something only allowed during times of famine, and the father was always allowed to take back his children for the same price as he sold them for. As I explained already, the Romans did everything to get children better placed. The practice was abolished in the Corpus Iuris Civilis though. It is better than just leaving your kid to die somewhere, when you cannot decide where it will end + you can not follow up on it.
And no, he could not sell his wife.
"By engaging into a marriage "cum manu" a woman would lose her suability(?) if she had it in the first place - "capitis deminutio"."
If you could explain what marriage cum mano means, a lot of problems of the ones translating the digests and others would be sovled. It is still not known what in manu really means (exept for what the historians copy and is utter BS).
And losing her suability - with which you refer to civil rights - is absurd, for she did not even have them before she went into the family. But, as I mentioned, in 167 B.C. a women could also get civil rights. Why then go under the protection of a male? For the male was the one legally bound when the woman made a contract. This means that, when a woman buys something, it is the pater familias who will be asked to pay. The woman is protected (the system is more complex than that, but I can now not explain everything to you at length). Just remember that when she loses her 'suability', she also no longer can be sued.
"And even in the times of the digests - do you honestly think there was such a thing as an independent+married woman by todays standarts?"
That's an historian speaking. Read the Digests, and do not apply to 'common sense' as learned to you when you were young. The historians never translated the Digests or other sources properly, and a lot of myths exist (I'd like to list you some, but the thread is long enough already and I'm running out of time atm, try again in a couple of days if you're interested
).
"What about the law of the twelve tables, the corpus iuris civilis and everything inbetween?"
That's writing down the precedents so people know what to expect when they go in appeal to praefectures and so the judges know what will be accepted by the praefecture and what not.
"And roman law based on precedents, wtf? Until written laws started gaining importance, roman law was based solely on custums. A principle "a similibus ad similia" was indeed taken into account, but roman law was certainly NOT based on precedent :\"
Costums? Roman law became costums when the praefecture broke down in the West and all the Emperors recepted the Roman laws. But I do not know from where you believe that the Roman law was all costum. Do you honestly believe that the Praefecture in Rome (= highest legal organ in the empire) knew the customs for the whole Roman empire? There was 1 Roman law, which was it's strength...
Edit: with the 'there was 1 Roman law' I mean that they applied their rulings the same regardless of origin. It depends though wether or not you had civil rights or not.
"Then there were the middle ages, where the only free-ish women were widows, and all those other ages right up until the downfall of the "american housewife". In the west."
True enough, in the middle ages a lot changed. When the Corpus Iuris Civilis and others were being translated, they were translated by men who wanted to justify their position in the society. Thus, they translated it with 'in potestate' meaning you being able to decide everything for your family etc.