Updated on May 9 at 9:30 a.m. ET

Former London Mayor Boris Johnson made his Monday case for why the U.K. should leave the European Union, saying “there is simply no common political culture in Europe.”

Here’s an excerpt from his speech:

It is we in the Leave Camp—not they—who stand in the tradition of the liberal cosmopolitan European enlightenment—not just of Locke and Wilkes, but of Rousseau and Voltaire; and though they are many, and though they are well-funded, and though we know that they can call on unlimited taxpayer funds for their leaflets, it is we few, we happy few who have the inestimable advantage of believing strongly in our cause, and that we will be vindicated by history; and we will win for exactly the same reason that the Greeks beat the Persians at Marathon —because they are fighting for an outdated absolutist ideology, and we are fighting for freedom.

That is the choice on June 23.

That’s the date on which Britons will vote on whether to stay or leave the EU. Prime Minister David Cameron, who, like Johnson, is Conservative, has made the case for why Britain should remain in the bloc. In a speech Monday, he said: “Isolationism has never served this country well. Whenever we turn our back on Europe, sooner or later we come to regret it. We’ve always had to go back in and always at a much higher cost.” Polls show a close contest ahead of the June referendum.

Here’s more on what the fight is about.