There are very few holidays celebrated throughout the Alliance, whereof these are a few:
Day of the New Century
Celebrated on the first day of each year, the Day of the New Century is a holiday recognized on the Alliance calendar. The tradition began at the beginning of the 4th century in the 5th Age, when the king of Calabria decided to create a new holiday to uplift the spirits of his people. Times were hard, and people would look for any excuse to celebrate. So the king (who happened to be turning 54 that year) decreed that this new century would be the greatest ever for the people of Calabria, and so starting on the first day they would celebrate it, each and every year. The concept of celebrating the new century every year spread like wildfire throughout the Alliance, that it quickly became an inter-dimensional holiday.
Heart’s Day is a holiday that finds its roots in the Aten Nations. An accurate translation continues to elude scholars and linguists, but the original Aten day may actually pre-date the Empire of Roads. In the Aten tongue, the name means roughly “to champion a love so strong that two hearts become one”. Evidence suggests that in the ancient times this was a solemn occasion upon which to honor couples who had been married more than two centuries. In more modern times (to the Aten, ‘modern times’ are defined as post-Mage Wars), it has evolved into a sort of celebration of love. Different regions celebrate it different ways, and few humans even realize it is not a human holiday at all, but in fact an extremely ancient Aten day.
The Heritage Festival began during the Kamian Succession Wars as a way for war refugees to celebrate and continue to honor their customs and cultures. By the mid Sixth Age, it was celebrated all over the Alliance, even in corners not touched by the war (which was still going until the mid-to-late Age). Perhaps the largest celebration of the festival takes place anually in Arindell, which has the most diverse population in the entire verse. The holiday takes place on the 29th and 30th of the 9th month of the year, with celebrations traditionally lasting all night. See Visuban Cluster for a variation of this festival.
Day of Dawn's Reflection
Wash Day began as a specifically Atayan holiday, though similar celebrations were common throughout the region and similar civilizations off-world. Wash Day is held on the last day of fall, the final day before winter. On the Atayan calendar(eventually adopted by the Alliance), this is also the last day of the year.
The specific purpose of the holiday is rooted in Atayan funerary customs and mourning rituals. Among the Atayans, it was considered very difficult to let someone go whom you owed a debt to or held a grudge against. With many deaths often coming in the winter months, and most Atayans being largely snowed in to their homes, it was an important cultural touchstone to end the year without any regrets. Traditionally on Wash Day, all debts were forgiven and all disputes settled, with the slate being "wiped clean".