"but in theory giving overlordship above all christian (catholic) rulers of the time"

how effective was it. Did the rulers of the time acept the overlordship?

How do you think this effected and perpetuated "Fuedal relationship" in general?

well, ing eneral not, however rulers of coutnries like Poland and Hungary which just have recently been vonverted to chritianity via Germany were of course udner great influence. when Richard I. was imprisoned by the Duke of Austria he forced him to swore vassalship to the name of the emperor, but it was more or less just symbolic, England was not the vassal of the HRE thereafter.

I would say very important - the HRE has already been mentioned.

The papacy at Avignon is another example - where the French throne needed the prestige of the papacy behind them to legitimize their claims - and simply replaced / appointed / kidnapped / murdered? popes until they got one that would support them and then held him hostage at Avignon.  That whole saga reflects how important it was for the HRE and France to each feel that they had legitimacy.  Tied to all of this are both French and HRE suport for the various antipopes.

As to the power of the popes themselves - some greater, some lesser - but the conflict between Frederick Redbeard and both Adrian IV and Alexander III is a good example of how they could - without armies under their own command - control the will of Europe (if only at times under pain of excommunication).

There is a good - if biased article at the Catholic Encyclopedia:  http://www.newadvent.org/cathen/06252b.htm - http://www.newadvent.org/cathen/06252b.htm

Lots of good material there - Check their index for other related articles.

I thought that was only after an interdict.

A friend of mine posted this at another site.  They were discussing the effect of Harald's excommunication and how it may have affected the outcome when William invaded England.   She said it much, much better than I could have.

Excommunication was a declaration that severed the outward bond holding the individual to his place in the Church and in the Christian community. It also severed the internal bond of the excommunicate to God because the sentence pronounced on earth was deemed to be ratified in heaven. (The Vatican still considers it a "spiritual sword" and the heaviest penalty that the Church can inflict.)

In the centuries after the Christianization of Rome, the forum externum (the public ecclesiastical tribunal) was distinctly separated from the forum sacramentale (the tribunal of sacramental penance). From the ninth century on, excommunication gradually became an increasingly powerful tool of spiritual government in the hands of the Papacy. In essence, it became a coercive measure that could be threatened or inflicted to secure the observance of fasts and feasts, the payment of tithes, the obedience of inferiors, the denunciation of the guilty, and to compel the faithful to make known to ecclesiastical authority matrimonial impediments and other information. It also enabled the Papacy to enforce its secular agenda.

The immediate effects of excommunication are expressed in two reasonably well known verses:

Res sacræ, ritus, communio, crypta, potestas,
prædia sacra, forum, civilia jura vetantur.

(Indicating that the excommunicate suffers the loss of the sacraments, public services and prayers of the Church, as well as the right to Christian burial. If he exercises power or authority he loses all jurisdiction over the Faithful and no longer may engage in ordinary social intercourse with members of the Faithful.)

Technically, the Faithful were barred from interaction with an excommunicate. This barred conversations and the exchange of letters, prayer in common with the excommunicated, marks of honor and respect as well as business and social relations. The Faithful could not share meals with the excommunicated. Conjugal law was suspended toward an excommunicate, and children, servants, vassals, and subordinates in general owed no duty of submission.

As a side note, an excommunicate who remained in that state for too long (usually a year and a day during the medieval period) was deemed an apostate and a heretic. Those who associated with such an excommunicate also would be suspected of being apostates and heretics. They would, moreover, be considered associates in sin and occasions of sin themselves.

http://www.renaissancedress.com/merchantbodice.htm -  

Frederic Barberossa (Redbeard) is my favorite emperor. His fight against papacy was interesting and in the end he outsmarted pope and, if believe ,  imprisoned him.
The next pope was more docile.

This continous struggle between church and state will set the stage  to what is probably the greatest European political achievement: the separation of the state and church.

From polish monarchs only one: Boleslaus the Bold (Boleslaw Smialy) known also as Boleslaus the Generous (Boleslaw Szczodry) and also know as the Boleslaus the Cruel (Boleslaw Okrutny). Here is a short note about him, it says also about importance of papacy:

"Boleslaus the Bold (1039-1081), the eldest son of Casimir the Restorer, obtained the royal title in 1076, after 18 years of rule as a prince, thanks to his support of the pope in the latter's dispute with the emperor Henry IV. Papal legates restored the metropolis of Gniezno and established a new bishopric (next to the old ones of Poznan, Wroclaw and Cracow) in Plock. Boleslaus conducted many wars and intervened in dynastic conflicts in Hungary and Rus. His strong-arm rule provoked opposition among the nobles, including the bishop of Cracow, Stanislaw of Szczepanow. The bishop was put to death for treason, which caused a revolt by the nobles. Boleslaus was excommunicated and in 1079 he had to abandon the throne and seek refuge in Hungary, where he died several years later."

I figure most realms in the Res Publica Christiana had at least one ruler excommunicated (appart maybe from those ass-lickers Castille). And yes, the Papacy had quite an influence over temporal powers in Medieval Europe. If not over the crowns itself, the imense network of priests and monasterys throughout the land assured their influence over the masses. Having a leader of a country excommunicated would infuriate a large crowd of believers. No one likes a big angry mob. So in order to avoid these complications it was best to put up with the Pope's indications and shut up. Most excommunications were temporary and revoged in a few months, since there was no real offence to the religious ways of the Papacy. Most excommunications are due to questions regarding financial rights and appointments to high positions in the national churches. Normally rulers would send their "doctors in law" to Rome to sort things out and achieve a friendly agreement. Or you could do like the Emperor or the French and elect an alternative Pope or wage war on the existing one.

As for my favorite example in these struggles between temporal and spiritual powers, none strikes as much as Frederick Roger's monumental "excommunicate this", when he went on to conquer Jerusalem through dilpomatic genious while excommunicated by Pope Gregory IX. 

Didn't know that! Wicked!

Suggested Reading:

The Crusades: Islam and Christianity in the Struggle for World Supremacy by Geoffrey Hindley. A intelligent book that is no just about the crusades by ranges from the Prophet Mohammed to the mid-15th century.

Wat zijn papacy? Ik begrijp ook niet dit niet. Doe papacy levend in Zuidelijk Europa of iets. Iemand te vertellen gelieve me wat papcy is. Ik wil over papacy in Europa leren. Ik dacht zij of iets volgens die lijnen Italiaans waren.