First-century Christians made good use of the Roman system of roads. Roman engineers constructed over 50,000 miles (80,000 km) of roads that linked nearly every province. The roads cut through forests, crossed deserts, and scaled mountains. In addition to their system of roads, the Romans could take advantage of some 17,000 miles (27,000 km) of navigable rivers and canals. Roman ships traveled some 900 sea routes that linked hundreds of ports. Christians could therefore travel throughout the Roman world. There were difficulties, but the apostle Paul and others could journey throughout the realm without passports and visas. There were no immigration and customs checks. Outlaws feared Roman punishment, so roads were relatively safe. Travel by sea was similarly safe because Rome’s navies kept sea lanes free of piracy.