Shape of the instrument
The nafir is a long, straight and valveless trumpet originally from the Middle East. It had been brought to Europe at the time of the crusades, where was renamed as añafil (a Spanish term).
This long trumpet was made of brass, gold, silver, or other metals and is currently used by the Muslim people of North Africa on the occasion of Ramadan and during the solemn processions that occur in June.
History of nafir
The best way to get an idea of how a nafir looked like is through this Arab miniature dating back to 1237:

There are two musicians blowing their nafir-s as they sit on the back of their horses.
As you can see from the miniature, the sound of the two trumpets was accompanied by drums.
The instrument lacked finger holes and could produce only partials of the fundamental tone.
According to the Encyclopaedia Iranica, the Persian nafir belonged to a group of long ceremonial trumpets called karna.
These trumpets were considered as an emblem of royalty and played a key role in a particular kind of musical ensemble known as naqqāra-ḵāna or nawbat.
The purpose of this group of musicians was to perform at specific times of day and on special occasions, such as battles and public celebrations after a military victory.
We find further evidence of the ceremonial use of a trumpet called nafir in the paintings of the Akbar Nama, a work focused on describing the ceremonial life at the Moghul court (1556–1605).
By examining the paintings and reading the text, one can get a clear description of how nafir was used as a tool to ritually mark the running of time.
If you want to examine the different kinds of nafir preserved in today’s museums, you can visit MIMO, a website devoted to explore the world collections of musical instruments.
Military and religious uses of nafir
The nafir is born to be employed as a signaling instrument to issue military orders into the battle field.
There’s no doubt about that.
Its depiction provided by the miniature confirms that the nafir was used to send out messages to armies and large crowds.
If you want to deepen the relationship between war and musical instruments in the ancient Muslim world, I suggest you this article by Said Bolta-Zoda Saidiy.
Nowadays this instrument marks the secular and religious functions of the Berber people, an ethnic group that lives in various parts of Africa, mostly in the northwestern regions.
We know that Muslim people from Nigeria play long and straight trumpets similar to the nafir.
In this field recording by Jenkins you can hear the sound of the Nigerian nafir:
Talking about the uses of the nafir in today’s world, it is noteworthy to mention that the particular shape of this trumpet has inspired the construction of ceiling lamps reminiscent of the musical instrument.