The concept of a police force operating independently of the military goes back to the Praetorian Guard of ancient Rome. In the Middle Ages, noblemen protected their estates by appointing constables to enforce the law and to arrest and guard criminals, but the first modern, organized police force was the London Metropolitan Police. Established in 1829, this organization became the model for law enforcement organizations in the United States and many other industrialized nations around the world. The presence of a police force serves to uphold the laws of society, and to control civil unrest. A strong, visible police force strengthens confidence of the community by keeping the citizens safe.