As a sign of peace, people in the crowd are encouraged to shake hands with those near them.
Over in the dignitaries section in St Peter's Square, President Trump can be seen shaking hands with those closest to him - including French President Emmanuel Macron.
As we've reported, Donald Trump is on the front row of the service today - it's arranged by the (French) alphabetical order of countries, meaning the États-Unis is near Finland, France, and Estonia. Historically, French was regarded as the language of diplomacy.
