I think that Coldplay's song Viva La Vida is about the memoirs of Napoleon as he was writing them in his second Exile. The name alone, Viva La Vida cannot be directly translated, but by mixing translations of Spanish and French, it could mean Living the Empty Life. The Album cover is a French portrait made during the final French Revolution
I used to rule the world
Seas would rise when I gave the word
Obviously a metaphor. It can be interpreted as many things, but mainly as Napoleon's rule and control of most of Europe.
Now in the morning I sweep alone
Sweep the streets I used to own
Napoleon was first exiled to Elba and disowned by the people. Again, a metaphor.
I used to roll the dice
Feel the fear in my enemy's eyes
Listen as the crowd would sing:
"Now the old king is dead! Long live the king!"
Rolling the Dice, meaning he called the shots and took them. He was the most feared and hated man in all of Europe and Russia. "Now the old king is dead! Long live the king!" The old king being one of two people: King Louis XVI or Robespierre, who interpreted himself as a god of the Republic.
One minute I held the key
Next the walls were closed on me
And I discovered that my castles stand
Upon pillars of salt, pillars of sand
Napoleon was emperor of France and knew what was for her best interest, but the royalty of Europe did not like Napoleon because he was not of royal blood. "The walls were closed on me" represents Europe rebelling during his rule, ultimately forcing him into exile. "Castles stand upon pillars of salt and pillars of sand" meant that there was only false recognition of hope in the people, as they would go along with what the more powerful invading country had to offer, as Europe declared war on the people of France, which forced them to turn their back on their Emperor.
I hear Jerusalem bells are ringing
Roman Cavalry choirs are singing
Roman Cavalry Choirs could mean his cooperation with the Holy Roman Empire. Jerusalem bells are ringing as he was greeted into Palestine and Israel.
Be my mirror my sword and shield
My missionaries in a foreign field
This obviously represents the way Napoleon talked to his troops, and called them his missionaries because he told them that they were on a mission to serve their country France. He knew his soldiers by name.
For some reason I can't explain
Once you know there was never, never an honest word
That was when I ruled the world
Never an honest word may relate to his relations with the Czar of Russia, Czar Alexander I. They were good friends, but he betrayed him in the end because he did not want to join Napoleon's Empire.
It was the wicked and wild wind
Blew down the doors to let me in.
Napoleon wasn't French. He was Corsican. He traveled to France after the demise of Robespierre and saw that the country was in ruins. He took advantage of this and joined the military. He went up in the ranks and soon became Consul of France, later emperor.
Shattered windows and the sound of drums
People couldn't believe what I'd become
The first line meaning the invasion of England, Russia, and Austria upon France. The Second line meaning the people couldn't believe that Napoleon expected the state of France to go up against the royal blood of Europe.
Revolutionaries Wait
For my head on a silver plate
Just a puppet on a lonely string
Oh who would ever want to be king?
Napoleon was forced into exile after France lost against the three invading Monarchies. Revolutionaries want to see him dead because of what he dragged France into. "Oh who would ever want to be king?" represents his doubts as he was writing his memoirs in exile.
I know Saint Peter will call my name
Napoleon used Roman Catholicism as a tool to win back the people of France. Under the reign of Robespierre, Catholicism was outlawed and the only religion was the Religion of the people, with Robespierre as the God. Napoleon gave back to the people what Robespierre took from them, but this should have been frowned upon by the Catholic Church, but the Pope said France could be re- entered into the church if Napoleon offers him protection and land. Napoleon did it for the advancement of France. He knew this was the right decision and was loved by the Pope. Saint Peter can be a metaphor for the Pope, being that he was the first pope. Pope Pius VII crowned Napoleon as Emperor, meaning he called his name.
That's my theory, but it may be wrong. I also like the Jesus interpretation. Hope this helps!