The surname Ardo is uncommon in Italy and is documented in small numbers especially in Piedmont, Emilia-Romagna and the Aosta Valley, as well as in some southern areas such as Campania. Its formation can be linked to the Germanic ending -ardo (from the old hardhu = "strong, brave"), present in numerous medieval names that later gave rise to various Italian surnames. These elements are known as onomastic elements, that is, components inherited from old personal names that function as roots or endings.

The ending -ardo was not originally a suffix in the modern sense, but a Germanic element incorporated into personal names, especially during the Lombard influence in Italy. From this root numerous surnames were formed:

• Belardo: ber(h) (bear) + hardhu, "strong bear".
• Bernardo: bern (bear) + hardhu, "brave as a bear".
• Everardo: ebur (boar) + hardhu, "strong as a boar".
• Gerardo, Gherardo: ger (spear) + hardhu, "brave with the spear".
• Riccardo, Ricciardo: ric (power) + hardhu, "powerful and brave".
• Viscardo: wis (wise) + hardhu, "brave and wise".

Over time, this ending also combined with Latin or Italian roots, giving rise to new compound surnames:

• Bacciardi: from Baccio + –ardi, "strong descendant of Baccio".
• Biancardi: from bianco (white) + –ardi.
• Bonardi: from buono (good) + –ardi.
• Giannardi, Giovanardi: from Gianni / Giovanni + –ardi.
• Leonardi: from leone (lion) + –ardi.
• Morardi: from Moro (dark-haired) + –ardi.
• Zanardi: from Zan (Venetian form of Giovanni) + –ardi.

Likewise, this element appears in gentilics (surnames indicating provenance):

• Lombardo: native of Lombardy.
• Luccardo: linked to Lucca or Lucardo.
• Piccardo: coming from Picardy (northern France).

Finally, the element -ardo was preserved in modern Italian in the formation of adjectives, often with a descriptive or even pejorative value:

• Bastardo: "illegitimate child".
• Bugiardo: "liar".
• Codardo: "coward".
• Gagliardo: "robust, vigorous".