The symbol of the digit 4, representing the four sacred elements, fire, air, water and land, has very old origins. 
For the ancient Persians the world was divided by a cross in four parts, where at the centre a source was standing. These were the origins of the CHAHAR BAGH, the persian garden divided in four (chahar) parts, and of the islamic court, enriched by a central fountain.
These courts were present in the calif palais as well as in simple houses, bazars, mosques and madrassas (theological schools).
Such an omnipresent plan described the unity, order and serenity of a closed space, centered on the divine gift of the water.