In 8th Century BCE, when the Romulus Calendar was used, there were only 10 months, with January and February missing. Each month had either 30 or 31 days.
Winter months weren’t counted as planters and harvesters didn't care for those unproductive, cold months, resulting in 61 days of non-calendared time, and years with only 304 days.

Early Roman Calendar

In 713 BCE, King Numa Pompilius introduced two new months, January and February, added to the end of the Calendar.
As February was the last month on the list, it ended up being short (28 days) while other months were also modified to be either 29 or 31 days.

Introducing January And February In Calendars

As the years went by, the Romans realized they had to add or subtract days to sync itself with the seasons. So many days were out of sync that they even had to add a 27-day leap month called Mercedonius.
The confusion reached its peak in Julius Caesar's time, resulting in a year that was 445 days long(in 46 BCE). Caesar aligned it and that is what is being followed even today.

Leap Year Problems

<div>February 1, 2017</div><figure><img src="https://images2.minutemediacdn.com/image/upload/c_fill,g_auto,h_1248,w_2220/f_auto,q_auto,w_1100/v1555449701/shape/mentalfloss/february_0.jpg" alt="iStock" width="768" height="431"><figcaption dir="auto">ISTOCK</figcaption></figure><BLOCKQUOTE><video playsinline="" webkit-playsinline="" muted="" style="height: 100%; left: 0px; display: block; width: 100%;"></video>Thirty days hath September, 
April, June, and November. 
All the rest have 31, 
Except for February, 
Which got the short stick because it's cold and no one likes it. &nbsp;</BLOCKQUOTE>Well, something to that effect. Some believe February once boasted 29 days and that Augustus Caesar stole a day so he could add it to August, which was named for him. (If there’s a month named after you, why not milk it?) But that’s a myth. Rather, February has 28 days because, to the Romans, the month was an afterthought. In the 8th century BCE, they used the Calendar of Romulus, a 10-month calendar that kicked the year off in March (with the spring equinox) and ended in December. January and February didn’t even exist:Martius: 31 days Aprilius: 30 days Maius: 31 days Junius: 30 days Quintilis: 31 days Sextilis: 30 days September: 30 days October: 31 days November: 30 days December: 30 daysTally up those numbers, and you’ll see a problem—the year is only 304 days long. Back then, winter was a nameless, monthless period that no one cared for much. (Planters and harvesters used the calendar as a timetable. To them, winter was useless and wasn’t worth counting.) So for 61 days out of the year, Romans could ask “What month is it?” and you could correctly answer, “None!”King Numa Pompilius thought that was stupid. Why have a calendar if you’re going to neglect one-sixth of the year? So in 713 BCE, he lined the calendar up with the year’s 12 lunar cycles—a span of about 355 days—and introduced January and February. The months were added to the end of the calendar, making February the last month of the year.But no Roman calendar would be complete without some good old-fashioned superstition mixed in! The Romans believed even numbers were unlucky, so Numa tried to make each month odd. But to reach the quota of 355, one month had to be even. February ended up pulling the short stick, probably because it was simply the last month on the list. (Or as <a href="http://www.straightdope.com/columns/read/442/how-come-february-has-only-28-days" dir="ltr">Cecil Adams</a> puts it, “If there had to be an unlucky month, better make it a short one.”) Numa’s calendar ended up looking like this:Martius: 31 days Aprilius: 29 days Maius: 31 days Iunius: 29 days Quintilis: 31 days Sextilis: 29 days September: 29 days October: 31 days November: 29 days December: 29 days Ianuarius: 29 days Februarius: 28 daysOf course, a 355-day calendar had its bugs. After a few years went by, the seasons and months would fall out of sync. So to keep things straight, the Romans would occasionally insert a 27-day leap month called Mercedonius. The Romans would erase the last couple days of February and start the leap month on February 24—further evidence no one ever cared much for the month. &nbsp;This caused headaches everywhere. The leap month was inconsistent, mainly because Rome’s high priests determined when it would arrive. Not only did they insert Mercedonius haphazardly, but the priests (being politicians) abused the power, using it to extend the terms of friends and trim the terms of enemies. By Julius Caesar’s time, the Roman people had no clue what day it was.So Caesar nixed the leap month and reformed the calendar again. (To get Rome back on track, the year 46 BCE had to be <a href="http://www.uh.edu/engines/epi2364.htm" dir="ltr">445 days long</a>!) Caesar aligned the calendar with the sun and added a few days so that everything added up to 365. February, which by now was at the top of the calendar, kept its 28 days. We can only imagine it’s because Caesar, like everyone before and after him, just wanted it to be March already.&nbsp;

Some believe February once boasted 29 days and that Augustus Caesar stole a day so he could add it to August, which was named for him. (If there’s a month named after you, why not milk it?) But that’s a myth.

Thirty days hath September, April, June, and November. All the rest have 31, Except for February, Which got the short stick because it's cold and no one likes it.

Well, something to that effect. Some believe February once boasted 29 days and that Augustus Caesar stole a day so he could add it to August, which was named for him. (If there’s a month named after you, why not milk it?) But that’s a myth. Rather, February has 28 days because, to the Romans, the month was an afterthought. In the 8th century BCE, they used the Calendar of Romulus, a 10-month calendar that kicked the year off in March (with the spring equinox) and ended in December. January and February didn’t even exist:

Martius: 31 days Aprilius: 30 days Maius: 31 days Junius: 30 days Quintilis: 31 days Sextilis: 30 days September: 30 days October: 31 days November: 30 days December: 30 days

Tally up those numbers, and you’ll see a problem—the year is only 304 days long. Back then, winter was a nameless, monthless period that no one cared for much. (Planters and harvesters used the calendar as a timetable. To them, winter was useless and wasn’t worth counting.) So for 61 days out of the year, Romans could ask “What month is it?” and you could correctly answer, “None!”

King Numa Pompilius thought that was stupid. Why have a calendar if you’re going to neglect one-sixth of the year? So in 713 BCE, he lined the calendar up with the year’s 12 lunar cycles—a span of about 355 days—and introduced January and February. The months were added to the end of the calendar, making February the last month of the year.

But no Roman calendar would be complete without some good old-fashioned superstition mixed in! The Romans believed even numbers were unlucky, so Numa tried to make each month odd. But to reach the quota of 355, one month had to be even. February ended up pulling the short stick, probably because it was simply the last month on the list. (Or as <a dir="ltr" href="http://www.straightdope.com/columns/read/442/how-come-february-has-only-28-days">Cecil Adams </a>puts it, “If there had to be an unlucky month, better make it a short one.”) Numa’s calendar ended up looking like this:

Martius: 31 days Aprilius: 29 days Maius: 31 days Iunius: 29 days Quintilis: 31 days Sextilis: 29 days September: 29 days October: 31 days November: 29 days December: 29 days Ianuarius: 29 days Februarius: 28 days

Of course, a 355-day calendar had its bugs. After a few years went by, the seasons and months would fall out of sync. So to keep things straight, the Romans would occasionally insert a 27-day leap month called Mercedonius. The Romans would erase the last couple days of February and start the leap month on February 24—further evidence no one ever cared much for the month.

This caused headaches everywhere. The leap month was inconsistent, mainly because Rome’s high priests determined when it would arrive. Not only did they insert Mercedonius haphazardly, but the priests (being politicians) abused the power, using it to extend the terms of friends and trim the terms of enemies. By Julius Caesar’s time, the Roman people had no clue what day it was.

So Caesar nixed the leap month and reformed the calendar again. (To get Rome back on track, the year 46 BCE had to be <a dir="ltr" href="http://www.uh.edu/engines/epi2364.htm">445 days long </a>!) Caesar aligned the calendar with the sun and added a few days so that everything added up to 365. February, which by now was at the top of the calendar, kept its 28 days. We can only imagine it’s because Caesar, like everyone before and after him, just wanted it to be March already.

Why Are There Only 28 Days in February?

Early Roman Calendar

Introducing January And February In Calendars

Leap Year Problems

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