Yes, it is true: there are so many documents you have to have to get married in Italy but this will be your only stress because you don’t have to think about anything else. Your  marriage will be supervised by a wedding planner who will think about all the aspects of your BIG DAY.
But let’s see together. American citizens must have a valid passport, birth certificate and a permission to marry (nulla osta). These documents must be translated into Italian and to be legal, the translation must be given by the Apostille stamp by the secretary of State in the State each document was originally issued, then obtain an Atto Notorio from an Italian consul in the US. This must been obtain and sworn by two witnesses. When you finally arrive in Italy you will sign another declaration this time sworn by the Us consul in Italy stating there is no impediment to your marriage. Legalization of the Nulla Osta must be done by the office of the Prefecture.
For the Australian citizens is simpler. They must be 18, both free, true consent must exist, the relationship must not be a prohibited one. The Australians marrying in Italy need a certificate of no Impediment, this certificate must be obtained.
Australians have to fill out an application for Certificate of No Impediment to marriage form, witnessed by a Justice of the Peace, a consular official at an Au diplomatic mission overseas or an officer of the Department of Foreign affair and trade. Present your birth certificate. Present these documents to the marriage office of the municipality.
Catholic requirements for marriages in Italy
1.Formal letter on church letterhead from your parish, stating that you have fulfilled the Pre Cana procedures and granting permission for the wedding to be performed in the church of…
2.A letter from the Archbishop or Vicar of the parish stating the same, the priest can obtain.
3.All certificate of baptism, first communion and confirmation sent together in the same envelope. Original of the marriage encounter with church seal signatures. Seals and stamp from the parish office so that everything look correct. please refer also to http://www.sayyesinitaly-tuscany.blogspot.com

Con tutto questo popò di roba ditemi voi se uno prende e dice:”lo sai i’cché e ci si sposa a casa nostra!” Invece no! Questi dal Giappone, dall’America, dall’Australia, dal Canada prendono baracche e burattini e vengono qui a dire “SI”, poi magari dopo due o tre anni si divorziano. Visto che però questa tendenza non cessa di esistere mi vien da pensare che forse i nostri uffici comunali fanno veramente in fretta a redigere tutti questi documenti, poi quando siam noi a dover andare in Comune a chiedere qualcosa si aspetta sempre un bel pò, ma si sa lo straniero paga e salatamente, noi anche, ma tanto siam concittadini e ci si passa sopra…