[5] An origin legend with considerable impact on Danish national historiography connects the introduction of the flag to the Battle of Lindanise of 1219.

The private company Dansk Standard, regulation number 359 (2005), defines the red colour of the flag as Pantone 186c.

A tradition recorded in the 16th century traces the origin of the flag to the campaigns of Valdemar II of Denmark (r. 1202–1241).

The oldest of them is in Christiern Pedersen's Danske Krønike, which is a sequel to Saxo Grammaticus's Gesta Danorum, which was written in 1520 to 1523.

The second source is the writing of the Franciscan friar Petrus Olai (Peder Olsen) of Roskilde (died c. 1570).

The Danes were all but defeated when a lamb-skin banner depicting a white cross fell from the sky and miraculously led to a Danish victory.

However the Danish bishop, Anders Sunesen, was on top of a hill overlooking the battle and prayed to God with his arms raised.

Bruhn interprets the story in the context of the widespread tradition of the miraculous appearance of crosses in the sky in Christian legend, specifically comparing such an event attributed to a battle of 10 September 1217 near Alcazar in which it is said that a golden cross on white appeared in the sky and brought victory to the Christians.

In the Gelre Armorial, dated c. 1340–1370, such a banner is shown alongside the coat of arms of the king of Denmark.

About the same time, Valdemar IV of Denmark displays a cross in his coat of arms on his Danælog seal (Rettertingsseglet, dated 1356).

The seal of Eric of Pomerania (1398) as king of the Kalmar Union displays the arms of Denmark's chief dexter, three lions.

The reason that the kings of Denmark in the 14th century began displaying the cross banner in their coats of arms is unknown.

Caspar Paludan-Müller (1873) suggested that it may reflect a banner sent by the pope to support the king during the Livonian Crusade.

[13] Adolf Ditlev Jørgensen (1875) identifies the banner as that of the Knights Hospitaller, an order that had a presence in Denmark from the later 12th century.

The legend attributing the miraculous origin of the flag to the campaigns of Valdemar II of Denmark (r. 1202-1241) was recorded by Christiern Pedersen and Petrus Olai in the 1520s.

Slesvig historian Ulrik Petersen (1656–1735) confirms the presence of such a banner in the cathedral in the early 17th century and records that it had crumbled away by about 1660.

Contemporary records describing the battle of Hemmingstedt make no reference to the loss of the original Dannebrog, although the capitulation state that all Danish banners lost in 1500 was to be returned.

In a letter dated 22 February 1500 to Oluf Stigsøn, King John describes the battle but does not mention the loss of an important flag.

In 1598, Neocorus wrote that the banner captured in 1500 was brought to the church in Wöhrden and hung there for the next 59 years until it was returned to the Danes as part of the peace settlement in 1559.

[citation needed] In 1886, the war ministry introduced a regulation indicating that the flag should be flown from military buildings on thirteen specified days, including royal birthdays, the date of the signing of the Constitution of 5 June 1849 and days of remembrance for military battles.

The size and shape of the civil ensign (Koffardiflaget) for merchant ships is given in the regulation of 11 June 1748, which says: "A red flag with a white cross with no split end.

At the same time, the Danish East India Company was allowed to fly the Splitflag past the equator.

From about 1750 to the early 19th century, a number of ships and companies in which the government has interests received approval to use the Splitflag.

Any swallow-tail flag, no matter the colour, is called a Splitflag provided it bears additional markings.

[19] The royal standard is the flag of Denmark with a swallow-tail and charged with the monarch's coat of arms set in a white square.

According to an article in the newspaper Nordjyske, the flag had been used in the former insignia of Flight Eskadrille 723 of Aalborg Air Base, in the 1980s.