Pope Leo just broke major security protocol with his popemobile entrance

Royals and major world leaders alike have gathered in Vatican today to witness Pope Leo's inauguration, but there's one key detail that's been spotted as Leo arrived on the infamous popemobile, and it could prove to be a pretty dangerous choice.

At about 8.15am, the newly elected pontiff was spotted on the open-top popemobile addressing the packed-out crowds which lined the streets of St Peter's Square ahead of the event, with viewers watching at home 'going nuts' for the interactions.

The first 'official' popemobile is widely considered to be a Mercedes-Benz Nürburg 460 Pullman given to Pope Pius XI in 1930, and came adorned with silk carpeting and embossed doves on the exterior.

But it wasn't until the 1970s that the nickname as we know it became popularised.

The popemobile has become a key way for the pontiff to interact with his followers, but it also serves another very important purpose - it's typically the pope's last line of defence against assassination attempts.

Pope Leo arrived at St Peter's Square in Vatican City on the open-top popemobile (David Ramos/Getty Images)

The vehicles often come complete with the option of bulletproof glass and heavy armour, coming after Mehmet Ali Agca attempted to assassinate Pope John Paul II in 1981.

At the time, Pope John was going about his regular routine of greeting his followers on St Peter's Square when bullets suddenly fired from the crowd.

Ağca shot the pope twice, leaving him severely injured, and was later sentenced to life behind bars.

To this day, his motives behind the attack remain unclear.

However, like his predecessor Pope Francis, Pope Leo has opted to ditch the bulletproof glass protection usually offered to pontiffs, despite the risks.

Speaking in 2014, Francis told Spanish media that he didn't like the glass 'sardine can' design of the protected vehicle as he felt it separated him from his followers. So, despite the risks, he opted for the open-top vehicle sans bulletproof protection.

And with Pope Leo having followed suit, it signals yet another break from tradition for the first American pontiff, after the 69-year-old spoke English at his first first mass following the conclave on 9 May.

An example of a bullet-proof popemobile (PATRICK BAZ/AFP via Getty Images)

The world looked on as they heard both his singing voice and notable Chicago accent, which is a Vatican first.

English is rarely used as the opening language of a papal homily, especially in such a formal and symbolically-loaded moment like the first mass in the Sistine Chapel.

After entering the basilica today for his inauguration, Pope Leo will be presented with two major items that symbolise his new papal powers at the Vatican.

The first of which is the Fisherman's Ring, which is named in honour of the first pope, Saint Peter - who was a fisherman. Additionally, he will also be presented with the pallium - a strip of lambswool which represents his role as a shepherd.

It is placed on his shoulders before the mass begins.

During the mass, Leo will deliver a homily (a religious sermon) to the public as he lays out some of the themes of his papacy.