I Am The Center of Gravity
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 invisible, 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 lie embalmed in the grave.
What am I?
The letter V