what am i

I am the center of gravity,hold a capital situation in Vienna, and as i am foremost in every victory, am allowed by all to be invaluable. Though i am invisable, i am clearly seen in the midst of a river. I could name three who are in love with me and have three associates in vice. It is vain that you seek me for i have long been in heaven yet even now i lie embalmed in the grave. What am I?