Alitalia makes use of the piece concept. Check the website for destination-specific regulations.
Within Italy, passengers are allowed to check in 1 piece of 23kg.
From Africa (except Seychelles) to everywhere (via Abu Dhabi) and vice versa:
Economy: 2 pieces of 23kg
Business Class: 2 pieces of 32kg
Infants are allowed up to 10kg of checked luggage.
Passengers are allowed 1 piece of hand luggage, not exceeding 8kg in weight with dimensions of 55(h) x 35(w) x 25(t) cm. In addition, you may bring onboard an accessory e.g. laptop, handbag.