Book excerpt: The Northeast Corridor between Boston and Washington is perhaps the single most significant stretch of railroad in the country, connecting dozens of cities like Baltimore, Philadelphia, and New York City. The line carries thousands of passengers daily on a mix of long-distance, regional, and commuter trains. Before it emerged as a vital stretch of railway, some of the earliest railroads in America created a foundation for the future corridor. They constructed a patchwork of lines that laid the groundwork for the Northeast Corridor of today, which later formed integral portions of the Pennsylvania Railroad and the New York, New Haven & Hartford Railroad. The impact of this line is still felt in the many communities that developed along the tracks. While the Northeast Corridor continues to evolve, it remains as relevant as it was when the original developers conceived the rail link nearly two centuries ago.