Sheltering from the midday heat in her yellow-painted bungalow, Chieftainess Mwenda speaks passionately about her mission to end child marriage in Zambia, starting first in her own chiefdom. Reigning over 111 villages in Zambia's far northern Luapula province, Mwenda said her attitude towards a long-standing custom of early marriage changed almost overnight, when, four years ago, she learned about the dangers of teen pregnancies."The doctors explained that there are numerous complications when a girl gets pregnant at a young age, so arising from that I got involved in the thought to push it further," said the elderly chieftainess, clad in a bright pink and yellow dress, in an interview at the modest home she calls her palace."No one should allow a child in school (to marry)," she said, seated in an armchair and flanked by her two watchful advisers, one of them sitting on a sack of maize.In this remote area, the word of the chief can have more impact than laws enacted some 800 km (500 miles) away in the capital Lusaka.Although marriage below the age of 21 is officially illegal in Zambia, the southern African nation has one of the highest child marriage rates in the world.More than 40 percent of girls in Zambia are married before they turn 18, according to the United Nations Population Fund (UNFPA), a rate that has remained steady for more than a decade.The practice has deep cultural roots, and girls most vulnerable are the poorest and least educated.In 2013, the government launched a campaign to end child marriage, led by the Ministry of Chiefs and Traditional Affairs, bringing together Zambia's more than 200 chiefs, who hold hereditary positions and reign over more than 70 local tribes.In Mwenda Chiefdom those who disobey the chieftainess' order have to pay a fine as punishment. It does not come cheap. Typically a goat or a bundle of banknotes can cost transgressors as much as the bride price that is paid to a girl's family by the groom."Child marriage was very common and could only be stopped by putting a regulation in place where people can be punished when they engage in such a thing," said the chieftainess in the dingy reception room of her house, perched on a bush-covered hill.She said other chiefs across Zambia, a southern African nation of about 15 million people, were learning from her experience and taking action to stop child marriage.Each year more than 15 million girls worldwide are married before they turn 18, the campaign group Girls not Brides says. In sub-Saharan Africa, more than a tenth of girls are married by 15, and four in 10 are married by 18, according to the Population Council, a U.S.-based non-profit organisation.Child marriage deprives girls of education and opportunities and puts them at risk of serious injury or death if they have children before their bodies are ready. They are also more vulnerable to domestic and sexual violence.In June, the U.N. Human Rights Council adopted a resolution calling for an end to child, early and forced marriage, and recognising child marriage as a violation of human rights.Ending child marriage by 2030 is one of the targets contained in the new Sustainable Development Goals (SDGs) to be adopted by world leaders at a U.N. summit later this week.Following ordersBut diplomatic resolutions need to be followed up by action on the ground, campaigners say.Pamela Nyirenda of the Population Council in Zambia said chiefs' rulings are an effective way to stop child marriage because people have no option but to follow their leaders' orders."In the areas where the chiefs have a passion for this, (child marriage) numbers have gone down," Nyirenda told the Thomson Reuters Foundation at her office in Lusaka.She said most Zambian chiefs, about 10 percent of whom are women, have now resorted to punishments such as fines to stop parents marrying off their children early.She is concerned, however, that better-off parents with a desire to follow tradition may still disobey chiefs' orders."If the parents have the capacity to pay off that fine, then to them it's nothing," she said.Traditional initiation ceremonies, which begin once menstruation starts and are meant to teach girls how to please their husbands in bed, are an important marker in the lives of Zambian girls but also push them into marriage too young."They look forward to (putting into practice) whatever they have been told," Nyirenda said. "But for them to be sleeping with a man they need to be married, so that pushes them into early marriage."Education is crucial to ending the custom, Nyirenda said, by lowering peer pressure among girls and their families as well as tackling ignorance of the consequences of child marriage.Back in Mwenda, the chieftainess agreed that education was the key to changing attitudes."Children can only be safe in a school environment. As long as they remain in school they are safe from marriage," she said. ..