I left my bag on the train.
'Dimenticato' — 'di-men-ti-CA-to'. Five syllables; stress on the fourth.
Report immediately at the station's Lost & Found ('Oggetti Smarriti') window or to a Trenitalia staff member when you realise you left something on a train.
'Ho dimenticato la borsa sul treno' uses the passato prossimo. 'La borsa' is bag/handbag. 'Sul treno' means on the train. Italian rail Lost & Found is centralised — Trenitalia maintains a national database of found items.
Ho lasciato lo zaino sul Frecciarossa.
I left my backpack on the Frecciarossa.
Specifies the train type — important for tracing.
Quale treno era? Il numero?
Which train was it? The number?
The agent will ask this — always know your train number.
L'ho lasciato al posto 14C, carrozza tre.
I left it at seat 14C, carriage three.
Specific seat information helps find the item quickly.
Trenitalia's Lost & Found ('Oggetti Smarriti') operates from Roma Termini and can be contacted at +39 06 5754 7947. Items found on trains are sent to the terminus station and held for 30 days. Trenitalia's website also has an online lost item report form.