It is commonly believed that the crimson saltire of the Flag of Alabama was designed to resemble the blue saltire of the Confederate Battle Flag. The Battle Flag was square-shaped, and Alabama's flag is sometimes shown as a square. The legislation that created the state flag did not specify if the flag was going to be square or rectangular. The authors of a 1917 article in National Geographic expressed their opinion that because the Alabama flag was based on the Battle Flag, it should be square. In 1987, the office of Alabama Attorney General Don Siegelman issued an opinion in which the Battle Flag derivation is repeated, but concluded that the proper shape is rectangular, as it had been depicted numerous times in official publications and reproductions.
However, the saltire design of the Alabama state flag also bears resemblance to several other flags. It is identical to the flag of Saint Patrick, incorporated into the Union Flag of the United Kingdom to represent the union of the Kingdom of Great Britain with the Kingdom of Ireland. This has led to other origins being put forth as possibilities.
Some hold that it owes its origin as a simplification of the Cross of Burgundy Flag used by the Spanish in the New Spain and as the basis of military flags. One example that was used in the future Alabama was that of the Regimiento de Infanteria de Luisiana which took part in the Battle of Mobile as part of the Gulf Coast campaign of the American Revolution. 
Another remote, but possible inspiration was the flag carried by Co. F 7th Alabama Cavalry. The regiment was the only Alabama regiment in Rucker's Brigade commanded by Col. Edmund Rucker of Tennessee, later Alabama, who became a prominent Montgomery businessman after the war. The flag of the brigade used a white background with a red saltire and charged with 13 blue/green stars upon this saltire. This flag was given to Co. F 7th Alabama Cavalry by Rucker in order for them to act as his Color Guard, and is currently held by the Alabama Department of Archives and History as part of its Alabama Civil War Period Flag Collection.  But, the flag carried by Co. F 7th Alabama was not an Alabama Flag, it was the flag made for Rucker's Brigade a month before the 7th joined his brigade; the 7th was color party only after September 24, 1864. A bunting flag that exists, in the white and red configuration with 13 blue stars, is not believed to be Alabama associated, but also tied to Rucker's Brigade.