When was the first leap year?

The first leap year was 1752

The first leap year in the modern sense was 1752, when 11 days were 'lost' from the month September with the adoption of the Gregorian calendar by Britain and her colonies. After 1752 we adopted the system still in use today where an additional day is inserted in February in years wholly divisible by 4, other than years ending in 00 with the exception of those divisible by 400 which are still leap years (like 2000). This is certainly not the first use of leap years, the Julian calendar we used before 1752 had a simpler system of leap years, and remember, no calendar is universal.