A Formula One racetrack is a sacrosanct environment. The two white lines marking the boundary of the circuit represent a physical and psychological barrier that shouldn't be crossed either deliberately or accidentally in any circumstances without express permission - as Mark Webber will attest after his penalty at the Singapore Grand Prix.

However, for every seemingly innocuous lift home on the back of a rival's machine, there are many examples from F1's past where racetrack intrusions have been controversial, contentious, or downright dangerous.

Ahead of the Indian Grand Prix, Crash.net looks back at some of Grand Prix racing's most infamous unauthorized on-track transgressions.

Animal Interventions

India's Buddh circuit is hosting its third and potentially last F1 Grand Prix in 2013, but its first race in 2011 was notable for the return of an almost forgotten blight on F1's past: animals on the track.

The first ever practice session at the Buddh circuit was suspended due to stray dogs breaching the circuit and running amok. Attracted to the circuit by the smell of food being cooked on construction workers' campsites, the dogs were able to slip through incomplete perimeter fences and gain access to the track.

The suspension of practice to allow for the removal of dogs in India marked the first time since the 1990 Mexican Grand Prix that a F1 session was halted due to an animal intervention. Putting out the red flags to clear animals from the track represents a modern concession to animal safety though, and invading critters of times past were much less fortunate.

In 1970 in Mexico City Jackie Stewart escaped injury when he hit a dog, and Stefan Johansson had a comparable let-off in 1987 when his McLaren was destroyed by a collision with a deer at the original ?sterreichring. When the track re-opened in 1997, the deer remained, resulting in Juan-Pablo Montoya's memorably abysmal 'Oh deer!' pun over team radio after a near miss during practice at the 2001 Austrian GP.

Groundhogs have been a frequent and unwelcome on-track addition at Montreal's Circuit Gilles Villeneuve, but common collisions have caused significantly more damage to the critters than the cars or drivers.

Perhaps F1's most tragic incident involving an animal came at the 1960 Belgian Grand Prix. Briton Alan Stacey, driving for Lotus, was struck in the helmet by a bird while lying sixth on lap 25 of the race. The ensuing accident killed Stacey instantly, marking the sole occasion when an F1 driver has lost their life due to an animal intervention.

Disgruntled Former Mercedes Employee

The 2000 German Grand Prix is fondly remembered for Rubens Barrcichello's maiden victory from 18th on the grid in a dry-wet classic around the old Hockenheim. One of the catalysts for this stunning charge through the field was not in the conventional race script though: the bizarre on-track amblings of a disgruntled former Mercedes Benz employee.

The race started inauspiciously for Ferrari, Barrichello a poor 18th on the grid after problems in qualifying and Michael Schumacher punted off the track into retirement at the first corner by Giancarlo Fisichella's Benetton.

The McLarens of Mika H?kkinen and David Coulthard duly charged away at the front of the field, while Barrichello scythed his way through the pack and into podium contention. On lap 25 however, the race was altered dramatically by an unprecedented turn of events.

A lone man was incredibly wandering along and across the track on the run-up to the Clark chicane - with cars flashing past at well over 200 m/ph. His white raincoat flailing around like a spectral cape, the man presented an unknown danger to the field, prompting the instant intervention of the Safety Car.

Murray Walker's memorable commentary described the action with wonderfully relished giddy abandon; "Fantastic development! That lunatic, whoever he is, is changing the complexion of the race!" And so he did, with the safety car closing up the pack and allowing Barrichello to leapfrog the hitherto dominant McLarens and claim a wildly popular victory through treacherous conditions in the second half of the race.

But who was the 'lunatic' intruder? Later identified as Robert Sehli, a 47 year-old Frenchman, his raincoat gave some clue as to his motivations, with the slogan, "Mercedes Benz, who knew about my health problems, offered me a job I could not do and then sacked me for physical ineptitude after 20 years service", scrawled across the back.

It later emerged that 15 seconds prior to the start of the race Sehli had tried to run on to the grid, but had been apprehended and ejected - only re-gaining the circuit by cutting a perimeter fence. Two races previously, at Magny-Cours, he had attempted something similar but had been restrained by the FIA Photographers' Delegate.

Determination unbound, Sehli finally made his point, with the presumably unintentional but happy (for him) result that the Mercedes-engined McLarens lost a certain victory due to his bizarre protest.

Religious Zealot

A classic race won by Rubens Barrichello after a stirring overtake-laden drive interrupted by the intervention of a madman on the circuit? For a bizarre example of life imitating life, look no further than the mirror-image companion piece to Hockenheim 2000: the 2003 British Grand Prix.

Barrichello had fluffed the start from pole position, ceding the advantage to Jarno Trulli and Kimi R?ikk?nen, but a wonderful pass around the outside of the Finn into the Abbey chicane set Barrichello fair to attack Trulli for the lead.

However, on lap 11, the television cameras picked up an incredible sight; a man running down the Hangar Straight into the path of oncoming cars. Dressed in a green shirt, a kilt and trailing banners and flags, this interloper presented not the passive worry of potential seen in Hockenheim, but a clear and present danger bordering on the suicidal.

Finally wrestled to the ground off the track by race marshal Stephen Green, the intruder was later revealed to be Roman Catholic priest Neil Horan, whose on-track 'protest' was marked by a placard stating, "Read the Bible. The Bible is always right". Horan served two months in prison for aggravated trespass, but the consequences for Silverstone were nearly even more severe - with the circuit's security coming in for heavy criticism from leading F1 figures including Bernie Ecclestone at a time when Silverstone's position on the calendar was highly precarious.

Horan's taste for intrusion also saw him detained while attempting to charge the course at the 2004 Epsom Derby, before notoriously intervening with the men's marathon at the 2004 Athens Olympics. A serial fruitcake, Horan was also arrested at the 2006 World Cup ahead of a planned protest, appeared on Britain's Got Talent in 2009 and was last seen prophesising the fall of the British monarchy at of the birth of Prince George of Cambridge.

Back at Silverstone, Barrichello, unlike at Hockenheim, was a victim of the Safety Car, which dropped him back to eighth. This was a surmountable problem for the Brazilian though, storming through the pack and memorably passing R?ikk?nen for the lead through Bridge 12 laps from home for another classic victory blemished by an infamous on-track transgression.

Mansell Mania

2003 wasn't the first time that Silverstone had come under critical scrutiny for its security arrangements though, and the height of Mansell mania in 1992 saw an emotionally charged and highly dangerous mass track invasion after 'Nige' won the 1992 British GP.

Mansell had famously won at Silverstone in 1987 and 1991, but the 1992 race took place in a frenzied environment, with Mansell's utter dominance allied to a huge championship advantage to create a carnival atmosphere around the home hero's charge to coronation.

Unlike Monza's endorsed mass-gatherings under the podium, the spectators at Silverstone broke ranks while the cars were still circulating, lining the start-finish straight as Mansell took the chequered flag before storming onto the circuit with cavalier disregard for the remainder of the field still circulating at racing speed.

The invasion was infectious, from a smattering of isolated fans at one moment to an overwhelming circuit-wide influx within seconds. The concept of safety in numbers provided an insulating blanket to the fans, but the lack of incident was merely a happy accident - especially with Gerhard Berger's engine expiring spectacularly as he toured home in fifth place.

Accosting Mansell at Maggots and Becketts, the crowd conjured a Union Jack for the Briton to flourish from his cockpit as he toured down the Hangar Straight, before the Williams was overwhelmed by the sheer mass of fans at Club Corner. Hoisted aloft by the hailing crowd, Mansell eventually required a police escort to even make the podium ceremony, where his dotingly sycophantic public drank in their hero's every fist pump with ecstatic glee.

It was a charmingly good-natured yet frighteningly irresponsible outpouring of collective ecstasy, and one of the reserved British public's most unbecomingly flamboyant expressions of communal sporting triumph.

Suicidal Pre-qualifying

The last of the spate of urban jungle street circuits that graced the United States in the 1980s and early 90s, Phoenix hosted three Grands Prix, of which the last, in 1991, was marred by a remarkably peculiar and dangerous on-track intervention.

With the race opening the 1991 season, the Friday morning pre-qualifying session would be the first on-track action of the new campaign. However, the action was red-flagged after only a few minutes after a man on crutches hobbled on to the track and laid down in an apparent attempt to commit suicide.

He was narrowly missed by Eric van de Poele, a Belgian driver making his F1 debut for the Lamborghini team.

"I couldn't believe it," van de Poole said. "It was my first laps in F1 and everything was supposed to be so professional. Then I came round the corner and there was a man lying in the middle of the track."

The man, named locally as 27 year-old Marlon Rauvelli, had been released from the Maricopa Medical Centre a few blocks away from the circuit earlier in the day. Rauvelli was subsequently taken back to hospital by the authorities, and pre-qualifying resumed.

The interruption clearly disrupted van de Poele's mojo though, as the Belgian finished plum last in pre-qualifying, a spectacular 8.7 seconds off the session pace, and 16 seconds off Ayrton Senna's ultimate pole position time.

Renegade Race Starter

Hans Heyer was an extroverted German racer who forged a respectable career in touring cars and sportscars, but is best remembered for one of F1's great guilty pleasure underdog stories; his illegal entry into the 1977 German Grand Prix.

For their maiden home race at Hockenheim, the fledgling German ATS team decided to enter a second car for the first time. Heyer, a notorious prankster who would only drive in two single-seater races in his entire career, was duly hired for his grand prix debut to help drum up support for the ATS cause.

However, driving the car for the first time, Heyer disappointingly failed to qualify after setting the 27th fastest time out of 30 runners.

Living up to his maverick reputation though, Heyer refused to be deterred. As third reserve should one of the starters suffer misfortune, Heyer lined his car up in the pits pre-race as the rules permitted at the time. The German though had a pre-meditated plan that certainly wasn't in the regulations, enacted with the friendly partisan support of a few myopic marshals.

When the flag dropped, Heyer brazenly blasted out of the pits and joined the race, making his grand prix debut to, incredibly, the complete ignorance of the authorities. The crowd cottoned on much faster than the officials, and roared their delight as the yellow ATS streaked off in pursuit of the field.

It was a short-lived ruse, as the gearbox on the car gave way after just 10 laps, but Heyer had pulled off a stunt that would be inconceivable by today's standards.

The stewards finally figured out what had happened only after Heyer's retirement, and he was subsequently disqualified from what would prove to be his one and only grand prix.

Heyer's F1 career therefore ended with the statistical tongue-twisting legacy of one race entered, one DNQ, one race started (illegally), one retirement and one DSQ - but more importantly gave the grand prix archives their most iconic have-a-go-hero story.

Will Saunders @formulawill