Rho is lapped by the river Olona and crossed by its tributaries Bozzente and Lura, nowadays partially cloaked inside the town.

Additional research during the 20th century showed that the town had remarkable importance during the imperial age, when it was part of the XI Transpadanian region.

Further archeological researches confirmed the existence in Roman age of the Via Mediolanum-Verbannus, a road connecting Milan to the Lake Maggiore, passing through Legnano and Gallarate.

In the piazza San Vittore an ancient cemetery and a Christian chapel has been found; in the current via Belvedere were discovered Capuchin graves with engravings of alfa and omega.

During the Lombard reign, the village assumed in its own topography names existing still nowadays; Pomero for example, from the Latin Post Moerus, meaning out of the walls.

Rho is first mentioned in a written document from January 9, 864 AD, a certificate of permutation by the notary Agatone, referred to the village simply as a bunch of houses under the name of Vicus Raudus, with a church entitled to Sant'Ambrogio and a rough castle.

Because of its water and fertile lands, in the 15th century many Milanese notables moved to Rho, building sumptuous palaces, mostly no longer existing.

According to the chronicles of that time, on 24 April 1583 a painting of Pietà cried blood tears, event subsequently recognized as a miracle by the Catholic Church.

During the police blitz, which took place after six hours, policemen mistakenly killed Sante Zennaro, who had heroically tried rescuing children negotiating with the kidnapper.

At the beginning of 21st century, the new exposition centre of Fiera di Milano was built inside an area for the 90% in the territory of Rho and for the remaining part in the township of Pero.

[7] Other names include: Rhode, Rodo, Raude, Raudo, Rhaudum; in 16th-17th century one common version was Aro,[8] then Rò, Rhò and Rho.

The coat of arms of the municipality is the wheel with five spokes, crest of the Capitanei de Raude family, vassals of the dukes of Saxony and Bavaria.