Rome is the top Italian destination for Easter week, or Settimana Santa, primarily because of the events led by the Pope in Vatican City and Rome.
Easter Week starts on Palm Sunday with a special mass said by the Pope in Saint Peter's Square, Vatican City. Although this event is free, the square is usually very crowded and it is hard to get admission. If you want to attend the Vatican Palm Sunday mass, get there early and be prepared to stand for a long period of time. The Blessing of the Palms, Procession, and Holy Mass for Palm Sunday take place in the morning, usually starting at 9:30, in Saint Peter's Square.
Holy Thursday Mass is held in the Saint Peter's Basilica, usually at 9:30AM. A Papal Mass is also said in the Basilica of Saint John Lateran, Rome's cathedral, usually at 5:30PM.