Iceland oldest cultural traditions are the annual sheep round-up which is carried on all around the countryside. The sheep are left to live freely in the mountains and valleys during the summer, after the season, the farmers ride to collect them with their sheep dogs. The round-up is held so they can sort the sheep all out as they can get mixed up after the free-living, each sheep is marked by their farmer. The farmers invite their family, friends and anyone who is interested to help them out during the round-up process. After the round-up is done there is a celebration known as Réttarball, a ball that is held to mark the successful sheep round-up, traditional singing, dancing, eating nice meals and drinking Brennivín (The Black Death). This is a very important event throughout rural Iceland and everyone is welcome to join.