"Is used" vs. "has been used" vs. "was used"

I have three sentences of which I'm not sure which one is grammatical, and why.

It refers to the Eiffel Tower.

• It is used as the symbol of Paris and of France for over a century.
• It was used as the symbol of Paris and of France for over a century.
• It has been used as the symbol of Paris and of France for over a century.

It has been used as the symbol... is correct here. Use Present Perfect when the action referred to started in the past, and either continues (or continues to have relevance) at the time of speaking.

"It has been used", because it's still "used as the symbol of Paris and of France".