addition, a wrestler can opt to roll out of the ring in lieu of tagging a partner or simply be knocked out of the ring, at which point one of his partners may enter. As a result, the tag team formula and pacing which has developed in U.S. tag matches is different from lucha libre because the race to tag is not a priority. There are also two-man tag matches (parejas) and "four on four" matches (atomicos). Masks Masks (máscaras) have been used dating back to the beginnings of lucha libre in the early part of the 20th century, and have a historical significance to Mexico in general, dating to the days of the Aztecs. Early masks were very simple with basic colors to distinguish the wrestler. In modern lucha libre, masks are colorfully designed to evoke the images of animals, gods, ancient heroes and other archetypes, whose identity the luchador takes on during a performance. Virtually all wrestlers in Mexico will start their careers wearing masks, but over the span of their careers, a large number of them will be unmasked. Sometimes, a wrestler slated for retirement will be unmasked in his final bout or at the beginning of a final tour, signifying a loss of identity as that character. Sometimes, losing the mask signifies the end of a gimmick with the wrestler moving on to a new gimmick and mask. The mask is considered sacred to a degree, so much so that fully removing an opponent's mask during a match is grounds for disqualification. During their careers, masked luchadores will often be seen in public wearing their masks and keeping up the culture of lucha libre, while other masked wrestlers will interact with the public and press normally. However, they will still go to great lengths to conceal their true identities; in effect, the mask is synonymous with the luchador. El Santo continued wearing his mask after retirement, revealing his face only briefly in old age, and was eventually buried wearing his silver mask. More recently, the masks luchadores wear have become iconic symbols of Mexican culture. Contemporary artists like Francisco Delgado and Xavier Garza incorporate wrestler masks in their paintings. Although masks are a feature of lucha libre, it is a misconception that every Mexican wrestler uses one. There have been several maskless wrestlers who have been successful, particularly Tarzán López, Gory Guerrero, Perro Aguayo and Negro