Like many crosses, the origin of the Amalfi Cross is obscure. It might have been brought to Amalfi, Italy, by Norman knights around 1025, and from there carried to Jerusalem by the Knights Hospitaller.
Over the next 400 years or so, the role of Hospitallers quickly changed. 'Crusading Knights' was a more apt title than 'Hospitallers', with their role to capture, lose, and re-capture again and again, both territory and influence from the Muslims.
Just as their weapons changed from defensive swords to offensive arrows, their cross changed from a simple Latin Cross (✝) to the more spiky arrow-head cross that appears today on the flag of Amalfi.
The Amalfi Cross is a particular form of Cross Pattée, equally well-known as a St. John's Cross or Maltese Cross.
Naval flag of Amalfi
On the current flag of Amalfi, a port 35km southeast of Naples, the croce di Amalfi is white on a blue field. (See other flags with crosses.)
Other emblems, such as the St John Ambulance logo, feature a white Amalfi Cross on a black field.
On that logo, the images of lions and unicorns between the cross arms are not to indicate the association specialises in animal welfare. St John do not train their supporters to treat lions... or unicorns. Rather, these beasts are supporters of the Royal Coat of Arms granted by the British Crown, and show 'St John' as being a Royal Order. (See other Medical Crosses)
The black originates from the colour of the monastic habits worn by brothers of the Hospitaller order in the 12th and 13th centuries. It was trendy in those days to bear a cross with pattée (splayed) arm ends, very similar to the Croix Fourche. White was the obvious choice to show against the black ground.
This order was founded by Benedictine monks and merchants from Amalfi, who re-established a hospital in 11th century Jerusalem. It was ostensibly to serve Italian pilgrims, but probably they also served other European pilgrims who hopped on the boat at Amalfi.
Coins of that period depict a similar cross, which may have influenced the brothers at the hospital. (The same cross pattern is found inside the Church of the Holy Sepulchre, next door to the Hospital.)
These coins can be seen at the Fitzwilliam Museum, Cambridge, England. In the centre of the obverse of the upper coin is the letter 'R', for King Roger II (1105-54), and on the reverse is a small cross with splayed arm ends. The lower coin shows IC XC NI KA surrounding a similar cross.
After the Crusaders conquered Jerusalem, the order was taken over and re-established as the Order of the Knights of Malta, who retained the distinctive Amalfi Cross.
We know of no artwork before the 16th century that shows the arrow-pointed cross in connection with the Order of St. John. And yet the style is more appropriate in depicting the role of the knights.
Initially, their role focused on providing physical sustenance in terms of food, lodging, perhaps medical support, and general tourist guidance. The brothers would also have been in a position to give spiritual guidance, whilst being sufficiently armed and ready to defend pilgrims against bandit attack. (See also St. Julian's Cross).
But very soon, 'Crusading Knights' was a more apt title than 'Hospitallers', with their role to capture, lose and re-capture again and again, both territory and influence from the Muslims.
As defenders of pilgrims against bandits, swords would be the weapon of choice. For defending or attacking a fortress in a Crusade, arrows would be required. Just as their armoury evolved from swords to arrows, their cross changed to the more spiky arrow-head cross that is familiar today.
For animal welfare societies, see the Blue Cross
Our favourite lion story: The Lion and Albert
As collective noun, we say a 'blessing of unicorns'. Why?
Also see Dr Michael Foster's page on the evolution of the Amalfi Cross at www.orderstjohn.org/osj/cross.htm. (Yes, even creationists use the word 'evolve' from time to time.)