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 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?

Enter your answer below and click Submit.