How is the Julius Caesar calendar different from ours?

The Julian calendar introduced by Julius Caesar had 365 days per year and 366 EVERY 4 years. This had allowed the calendar to creep out of line with the seasons.

The Gregorian calendar we use now has the leap year rule:

Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100; the centurial years that are exactly divisible by 400 are still leap years. For example, the year 1900 was not a leap year; the year 2000 was a leap year.