The River of Pisa is a river in Italy that flows through the city of Pisa. It is also known as the ARNO, which is a four-letter word that is one of the solutions to the crossword. The ARNO is the main river of Tuscany and is the third longest river in Italy. It originates in the Apennine Mountains and flows into the Ligurian Sea near the city of Livorno. The ARNO has been an important source of water for the city of Pisa since ancient times.