On this day in 753 B.C., Romulus founded the city of Rome (and in the process killed his twin brother Remus). So today (according to my calculations) is the 2758th birthday of Rome (though the web sites that I have found call it “2759° Natale di Roma”, so I might be one year off there).
2758 AUC, rock on.
753 is definitely the right year of the foundation. This Rome’s 2759th year in existence, so perhaps that is what those websites mean. Either that or they forgot that there is no year 0.
I believe that this year is 2759 AUC, which might explain the confusion – 753 BC was 1 AUC, and so was 2758 years ago.