RIYADH — Google Doodle on Wednesday joined in the celebrations to mark Saudi Arabia's 90th National Day with portraying its distinctive green flag. The doodle of the Kingdom's flag on the search engine giant's homepage featured the sixth and the final version of the flag, which was adopted during the reign of King Faisal in 1973. The National Day marked the 90th anniversary of the issuance of a royal decree issued by King Abdul Aziz for the unification of the country under the name of the Kingdom of Saudi Arabia. The national flag is in forefront of the celebrations of the Kingdom's National Day every year. It is hoisted in front of all government buildings as well as at many homes and cars. It is the symbol to manifest patriotism, love and loyalty to the nation as well as to its leadership. The green flag, featuring in white an inscription of the Islamic creed or Shahada and a sword. The green of the flag represents Islam and the sword stands for the strictness in applying justice. The Saudi flag boasts of having a rich and long story until it took the current shape and design. The story of its evolution consists of six phases; each has a different artistic design, well suited to the political events featuring the epoch of each phase. The first phase began with a green background and a white crescent in the middle, and it was flying since the first Saudi state, known as the Emirate of Diriyah during the period between 1750 and 1818. With the beginning of the expedition of King Abdul Aziz to Najd and conquering it, he adopted the Saudi flag, removing the crescent, and replaced it with the first part of Shahada or the Islamic declaration of faith "There is no God but Allah" on the total green background. The Shahada was written in white script, with a white space to the left of the flag, which is what it is known as the flag of the Emirate of Najd since the time of the King's entry to Riyadh in 1902 until 1921. During the time of King Abdul Aziz annexing many provinces, the country was known as the Kingdom of Najd during the period from 1921 until 1926. During this period, the flag was changed, and the word of monotheism "There is no God but Allah" became large on the green space, and the white part became the longitudinal right of the flag, and the white sword was added below the word of monotheism. During the fourth phase of the flag, the sword was removed, and the green flag was surrounded by white, with the word of monotheism in the middle. This flag was hoisted during the period from 1926 until 1932 in the Kingdom of Najd and Hejaz. Then, began the fifth and important phase in the history of the flag and this was after the announcement of the establishment of the Kingdom of Saudi Arabia in 1932. The flag became completely green, and the word of monotheism was written entirely in white, and below the Shahada was a white sword. The sixth and last phase of the Saudi flag was during the reign of King Faisal in 1973 and the King standardized the flag designed by Hafez Wahba who made some minor changes in the sizes of the flag and the word of monotheism. He also changed the beginning and end of the white sword, with the handle, at the bottom of the beginning of the word of monotheism and its end towards the mast, a sign of the end of the fighting, and thus becoming a symbol of strength and fortitude. The flag is designed in a rectangular shape, its width is equal to two-thirds of its length, and the background is green, with the phrase "There is no God but Allah, and Muhammad is the Messenger of God" in the middle of it in the calligraphic Thuluth script, and under it is an Arab sword, with its handle facing towards the flagpole. The flag is manufactured with identical obverse and reverse sides, to ensure the Shahada reads correctly, from right to left, from either side. The sword also points to the left on both sides, in the direction of the script. When viewed from the obverse front side, the flag is hoisted to the left of the flagpole. The flag is distinguished from the rest of the world's flags by not lowering it to half-mast as a sign of mourning or other occasions. It also does not bend to senior guests while inspecting the guard of honor, showing respect to Shahada.