Pope Benedict XVI has celebrated his last scheduled public Mass following his resignation. The service was for Ash Wednesday and was held in St Peter's Basilica. Looking tired, the 85-year-old pontiff anointed the foreheads of the faithful with ashes in a service attended by cardinals, bishops, monks, friars and pilgrims. Wearing purple vestments, he referred to his resignation in his homily, asking for the prayers of the faithful. Ash Wednesday marks the start of Lent, the most solemn season in the Church calendar that ends with Holy Week and Easter Sunday. The pontiff had originally been scheduled to celebrate Ash Wednesday at the small Sant' Anselmo church, then lead a procession to Santa Sabina Basilica on Rome's Aventine Hill. But the Mass was relocated to St Peter's to accommodate the crowds, the Vatican said. The change also saved the Pope the effort of the procession. Earlier, the Pope was cheered by crowds as he entered and began speaking at his weekly general audience at its traditional venue, the audience hall in the Vatican. Thousands of people gathered in the hall to greet him, giving him a standing ovation as he arrived, and cheering as he began and finished speaking. Looking tired and drawn, Pope Benedict thanked the crowd for their warm greeting and their sympathy. He said he was aware of the gravity of his decision to resign but also of his declining strength, adding that he was certain the Church would sustain him with prayer.