Below is an excerpt on the history of the origin of islamic calendar. The purely lunar calendar is known as qamariya (arabic qamar means the moon). It is also known as hijri calendar from the arabic word hegira,
 which means emmigration. The Prophet Muhammad pbuh, did not order 
anything regarding islamic calendar as an administrative or civil tools 
for time reckoning. He only put an example on how the beginning of 
(certain) islamic months be ascertained.
At the time of Khulafaur 
Rasyidun (The Guided Leaders), administrative system of Islamic monarch 
was trimmed little by little., according to the current administrative 
system around the world., as long as the system did not break the 
shari’a. The correspondences had been done repeatedly. But the problem 
was that the muslims did not have a stable counting of the years. Hence,
 sometimes each of them had different naming of the years. This happened
 during the time of caliph Abu Bakr -may Allah be pleased with him- , 
and several years of the reign of Umar -may Allah be pleased with him- .
 Thus we know the term ‘year of Tha’un’, since in that year, the 
epidemic of Tha’un occurred and spread to various regions.
Until 
finally, at the third year of Umar’s reign, there came a letter from Abu
 Musa Al Ash’ari -may Allah be pleased with him- a companion whom was 
appointed as the governor of Bashra, which content was: “Indeed, the 
letters from The Leader of the believers (Umar) often comes to us. But 
we don’t know, when shall we carry out the instructions inside it. Once 
we got a letter written in the month Sha’ban, but we did not know 
whether it was the present Sha’ban or the past year.”
When the 
letter reached him, Umar Ibn Khattab -may Allah be pleased with him- 
gathered the senior companions at once to discuss about the issue. This 
meeting took place in 20th of Jumadil Akhir, year 17 of Hijra. They 
agreed about the urgency of date establishment process as the reference 
of Islamic calendar, started from the establishment of the first year. 
Some suggested the year of birth of the Prophet -may peace and blessings
 of Allah be upon him- as the first year, the other suggested the year 
when he was assigned as the messenger of Allah, others suggested to use 
the Roman or Persian calendar, and some other suggestions being raised.
Finally,
 a decision was made based on the opinion of Ali Ibn Abi Thalib -may 
Allah be pleased with him- who suggested the year of the moving (hijra) 
of the Prophet -may peace and blessings of Allah be upon him- from Mecca
 to Medina, as the first year. Whereas the decision of establishment of 
the first month was taken from the opinion of Uthman Ibn Affan -may 
Allah be pleased with him-, who proposed to make the month Muharram as 
the first month in Islam, because such month is the beginning of year in
 the Arabic calendars before Islam.
Beside that, Muharram is one 
of the four holy months and the muslims would be just finishing their 
pilgrimage at that time. The establishment of Muharram as the first 
month of Hijra calendar was also based on the assumption that at such 
month, the Prophet -may peace and blessings of Allah be upon him- had 
not accomplished the hijra and he reached Medina before the next year 
Muharram. He started the hijra at the end of month Shafar, and he 
reached the gate of Medina on Monday, 8th Of Rabiul Awal, then he 
entered Medina on Friday, 12th of Rabiul Awal. The establishment of the 
beginning of Hijra calendar coincided the Friday, 16th of July, 622 AD.
(Taken from “Al-Mufasshal fi Raddi ‘ala Syubuhati A’da Al-Islam, 5:238)
From
 the origin of it’s naming, this calendar is well known by “qamaria/moon
 calendar”, because the principle or the basis of establishment of this 
calendar was the rotating cycle of the moon. This calendar is also named
 as Hijra calendar, due to the history of it’s establishment was related
 to the hijra of the Prophet -may peace and blessings of Allah be upon 
him- from Mecca to Medina.
(Source: Al-Habib) 
 


