It will work, but probably not very well. I do not see an 1800 ONLY carrier listed for Italy on the gsm world page. But, that could be old. The forum members in Italy will be in a better position to answer that question. Personally I would not go to Europe without a phone with the 900 band.
http://www.gsmworld.com/roaming/gsminfo/cou_it.shtml
Phones: Xiaomi Mi Mix 2, Samsung Galaxy A50, ASUS zenfone 3,
Sim cards: AT&T (Contract), 3 UK, Piranha Mobile