Argentina's railway network is unique because it utilizes a "multi-gauge" system, a legacy of the various private British and French companies that built the lines in the 19th and 20th centuries. The predominant gauge is the "Broad Gauge" (1,676 mm or 5 feet 6 inches), which is used by the major lines like the Mitre, Roca, and Sarmiento railways connecting Buenos Aires to the surrounding regions. There is also a significant "Meter Gauge" (1,000 mm) network, primarily the Belgrano Railway, which serves the northern parts of the country. Additionally, the "Standard Gauge" (1,435 mm or 4 feet 8.5 inches) is used by the Urquiza line in the northeast. There are even small sections of "Narrow Gauge" (750 mm), most famously the "Old Patagonian Express" (La Trochita). This lack of a single national standard has historically made it difficult to integrate the different regions, often requiring passengers to change trains or cargo to be reloaded. In recent years, the Argentine government has focused on refurbishing the broad gauge and meter gauge lines to improve freight efficiency and passenger comfort across the vast national territory.