Elise and Brooke Fiannaca turned 12 on Wednesday, on the 12th day of the 12th month of the 12th year of the century.
The unique and special circumstance of the celebration, the last day for the next 88 years in which each numeral in the date is identical, wasn't immediately apparent to all.
"Their father thought about that when they were born, but I didn't," said Mary Fiannaca, the twins' mother.
The number 12 has prominence in many cultures, including the 12 apostles, 12 gods of Olympus from Greek mythology and the universally accepted 12-hour time clock.
Twelve is also one of few numbers that can be evenly divided by so many other numbers, such as 1, 2, 3, 4, and 6.