The timing for Tango is 4/4, and there are usually 128 - 132 beats per minute. The rhythm is Quick-Quick-Slow, and the music is medium tempo orchestral, often march-like.
Originally the Tango was a light spirited Flamenco dance from Spain. With the Spanish conquest of much of South America, this Tango together with other Spanish folk dances naturally emigrated with settlers from Spain. Later there was a merging of this style and the Tangano, an African dance imported with the negro slaves, and then in Argentina in the slums of Buenos Aires in the late 19th Century, they became merged with the Habanera, a folk dance from Havana in Cuba. The resulting dance became known as the Milonga.
Although initially popular with the lower classes of Argentine society, the Milonga Tango had a most disreputable reputation for being developed in the backstreets and bordellos of Argentina. For over 100 years it was considered far to risqué for a dance hall. However, by the turn of the 20th Century, it had gained acceptance with the upper classes as it was cleaned up considerably, and started to become fashionable in Europe.
It's importation into the upper classes of Western Europe was catalysed by France's greatest music-hall star: Mistinguett, who gave the first ever demonstration in Paris in 1910. Interest in the dance rapidly exploded as "Tangomania", initially through Paris, then London and New York. The first world war did nothing to cool this interest, with Rudolph Valentino popularising the Tango further in his film "The Four Horsemen of the Apocalypse" (1921). More recent film demonstrations have been given by Al Pacino and Gabrielle Anwar in "Scent of a Woman" (1992), and by Arnold Schwarzeneggar and Tia Carrere in "True Lies" (1994).
The character of the Milonga Tango was of a very soft private dance, with visual emphasis on the leg movements. This character was changed dramatically in Paris in the 1930's, where the dance was combined with the proud torso of the other ballroom dances, and given a staccato action. This moved the visual emphasis to the torso and head, a characteristic which remains to this day. The intensity and drama of today's Tango comes from the predatory, cat like movement when walking. It is a dance of both domination and seduction, the secret of which lies in the posture and hold.