Question: What type of arts that have existed since ancient times did the Stieber Twins specialize in?

Context:
Luzzu
A luzzu (] ) is a traditional fishing boat from the Maltese islands.
 They are usually painted in bright colours, while the bow has a pair of eyes.
 Luzzus have existed since ancient times.
Lullaby
A lullaby, or cradle song, is a soothing song or piece of music, usually played for or sung to children.
 The purposes of lullabies vary.
 In some societies they are used to pass down cultural knowledge or tradition.
 In addition, lullabies are often used for the developing of communication skills, indication of emotional intent, maintenance of infants' undivided attention, modulation of infants' arousal, and regulation of behavior.
 Perhaps one of the most important uses of lullabies is as a sleep aid for infants.
 As a result, the music is often simple and repetitive.
 Lullabies can be found in many countries, and have existed since ancient times.
History of espionage
Espionage, as well as other intelligence assessment, has existed since ancient times.
Godalming Hundred
Godalming was an ancient hundred in the south west of the county of Surrey, England.
 It corresponds to the central third of the current borough of Waverley and some parts of the current borough of Guildford.
 Broadly speaking it extended from Guildown in the north to the border with Sussex in the south.
 Local people maintain the notion of the hundred, sometimes colloquially referred to as "Godhelmia", mainly because of the predominance of north/south routes of communication through the area that have existed since ancient times.
 As recently as 1995 there were proposals (from Surrey County Council) to recreate a local government unit based on the old hundred borders.
Ich Lebe Für Hip Hop
"Ich Lebe für Hip Hop" (English: I Live for Hip Hop ) is a single by DJ Tomekk, released in 2000.
 The song features GZA, Curse, Prodigal Sunn and the Stieber Twins.
 With the exception of repeating the songs title, Prodigal Sunn and GZA rap in English.
 Curse and the Stieber twins rap in German.
 The song peaked at No. 11 in Germany.
Little and Lesnes Hundred
Little and Lesnes was a hundred, a historical land division, in the county of Kent, England.
 It occupied the northern part of the Lathe of Sutton-at-Hone, within in the west division of Kent.
 Little and Lesnes was the northernmost hundred in the whole county of Kent.
 The hundred existed since ancient times, before the Domesday Book of 1086, until it was made obsolete with the creation of new districts at the end of the nineteenth century.
Stieber Twins
The Stieber Twins are a duo from Heidelberg, Germany, consisting of the brothers Martin (Marshall Mar, a.k.a. Martin Jekyll) and Christian (Luxus Chris a.k.a. Christian Hyde).
 They are known as graffiti artists, breakdancers, rappers, hip hop producers and DJs.
Mathematical fiction
Mathematical fiction is a genre of creative fictional work in which mathematics and mathematicians play important roles.
 The form and the medium of the works are not important.
 The genre may include short stories, novels or plays; comic books; films, videos, or audios.
 One of the earliest, and much studied, work of this genre is , an 1884 satirical novella by the English schoolmaster Edwin Abbott Abbott.
 Mathematical fiction may have existed since ancient times, but it was recently rediscovered as a genre of literature; since then there has been a growing body of literature in this genre, and the genre has attracted a growing body of readers.
 For example, Abbot's Flatland spawned a sequel in the 21st century: a novel titled "Flatterland", authored by Ian Stewart and published in 2001.
Graffiti
Graffiti (plural of "graffito": "a graffito", but "these graffiti") are writing or drawings that have been scribbled, scratched, or painted illicitly on a wall or other surface, often within public view.
 Graffiti range from simple written words to elaborate wall paintings, and they have existed since ancient times, with examples dating back to Ancient Egypt, Ancient Greece, and the Roman Empire.
History of engineering
The "concept" of engineering has existed since ancient times as humans devised fundamental inventions such as the pulley, lever, and wheel.
 Each of these inventions is consistent with the modern definition of engineering, exploiting basic mechanical principles to develop useful tools and objects.

Answer: Graffiti