The standard gauge in most countries is 1,435 mm while

The standard gauge in most countries is 1,435 mm while in Russia the railroads have a gauge of 1,524 mm. That gauge was finally adopted when the first main-line Moscow St. Petersburg railway was under construction (18421851). Thus Russia was the world's first country where the uniform gauge was adopted for all railways. In America, the gauge was unified only in 1886.