IMOLA, Italy - Thousands of Formula 1 fans gathered on Thursday (May 1 2014) for a commemoration event at the Imola circuit 20 years to the day after Brazilian driver Ayrton Senna was killed there.Dozens of enthusiasts drove their own cars around the Enzo and Dino Ferrari circuit to mark the anniversary of the tragic 1994 San Marino GP. Ferrari drivers Fernando Alonso and Kimi Raikkonen weredue to attend a ceremony later in the day for the man seen as one of the greatest drivers of all time.Video tributes to SennaMarco, a 31-year-old Italian F1 fan who was at Imola as a boy on the day of the crash, told AFP: "Our hearts sank when they told us the news." Marco wore the same type of helmet that Senna had on that day and was taking his car around the circuit.'GREAT ENCOURAGEMENT'Daniela, 39, from Belo Horizonte in Brazil, said: "What moves me about Senna was his humility, his enormous charisma. He is in our hearts like family."Another Brazilian fan, 57-year-old Renato, said: "His will to win was what I liked about Ayrton. He proved that a Brazilian could be internationally known and that was a great encouragement for us."Another Marco, 34, was wearing a chequered flag around his shoulders: "He was the best driver ever."A Catholic priest led a memorial service the previous day at the Tamburello corner where the triple F1 champion's Williams car careered off into a concrete barrier on lap seven at more than 300km/h and was later flown to Bologna hospital where he was pronounced dead at 6.40pm local time on that ill-fated Sunday.Thursday's ceremony came after a week of commemorative events held to mark the tragic accident which ushered in a raft of changes to improve F1 safety.Football club Corinthians from Sao Paulo, the city where three-million people turned out for Senna's funeral, paid tribute to their local hero by wearing crash helmets with the Brazilian flag colours before kick-off in a match against Nacional-AM on Wednesday.'BLACKEST WEEKEND'The Senna anniversary was made all the more poignant as another great F1 driver, seven-times champion Michael Schumacher, continues his fight for life after fracturing his skull in a skiing accident on December 29 2013. Ironically, it was Schumacher who went on to win the Imola race in which Senna was killed.Senna's death, the day after Austrian rookie Roland Ratzenberger was killed and two days after fellow Brazilian Rubens Barrichello was injured, was F1's blackest weekend.*"He was an incredible legend," said 2008 F1 champion Lewis Hamilton. "You like to think that one day you may be recognised as somebody who was able to drive similarly to him."Ferrari's Fernando Alonso said: "On my schoolbooks I didn't have pictures of girls - I was too young - but I had Ayrton there and in my room."Senna's sister Viviane told AFP this week that her brother's legacy was alive and well through the Ayrton Senna Institute which she chairs. She recalls a conversation she had with him some weeks before his death in which he told her how he wanted to contribute to a better future for Brazil by helping to open up opportunities for children.EXTENSIVE SAFETY CHANGES"Ayrton really wanted Brazil to work, for everyone to have a chance and from this dream the Institute was born," Viviane said. "We are working with more than two-million children and training some 75 000 teachers a year across around 1000 cities across Brazil."Senna's death prompted extensive changes, including the reform of the Grand Prix Drivers' Association. Engine capacities were reduced and tethers to help prevent wheels flying off during a crash were introduced.The HANS device to protect drivers' heads and necks was made compulsory and track run-offs were extended and improved. The must have worked: No F1 driver has been killed since Senna's death.*Not true: In 1928 the most serious Italian racing accident to date killed driver Emilio Materassi and 27 spectators at that year's Monza GP. The 1933 race killed three drivers.Stay with Wheels24 for the 2014 F1 season – fresh reports every day.