A Synopsis by Franco Baseggio
The origin of the Baseggio name is not certain, as there are two versions of the history. It is possible that there are two separate origins and that both histories are correct.
The main version of the history is that the original name BASILI, derived from the Greek Basileys, meaning “king”, was the name used by the Roman family from which we descended. The name changed various times after the Basili moved to Venice, Trieste, and other parts of Italy. Early versions were BASILIO, BASEGI, BASELLO, BASEIO, BASEI, BASEO, BASILEO, BASEJO, WASILEO, BASEGIO, BASILEJO, and BASEGGIO.
At some point both the Baseggio and Basilejo versions became entitled to use the honorific “de” before their name, thereby becoming de BASEGGIO, and de BASILEJO. Many of these variations are probably due to the different pronunciations and letters used in the parts of Italy where the family lived. For example, Basegio, when pronounced in Venetian, becomes Baseio. The “correct” usage eventually became BASEGGIO or de BASEGGIO.
The second version of the history has it that a Venetian family named MASTALITIA or MASTALIZIA had a church built to honor St. Basilio at the end of the 10th century. As a result, they were allowed to use the name Basegio, later Baseggio. I hypothesize that there was already a Basegio name at the time and that the Mastalitias preferred to use it because of its prestige.
In more recent times, the name has occasionally devolved to BASEGIO, BASSEGGIO, BESEGGIO, and BAZEGGIO. This has typically been the result of simplifications or misspellings by government authorities.
There are two interesting variations. The first is that a Baseggio who participated in the Crusades stopped off on the island of Santorini, Greece, and formed a branch of the family there which became known as BAZAIOS or variations of that spelling. BASEO and BAZEO seem to be the most common currently used versions of this Greek name. The second interesting variation is that an Italian Baseggio emigrated to Brazil in the late 19th century and, apparently, changed his name to BASILIO.
Sources: "History of Trieste" by Father Ireneo of the Cross, "Il Cappellari", Campidoglio Veneto, "Genealogie delle Tredici Casate" by Luigi de Jenner, "Le Tredici Casate" by Sergio Sghedoni and Marco Dorian.