This passing year contained an important sesquicentennial for Washington, one that -- if contemporary technology and corporate imperatives had been different -- would have been marked by civic ceremonies and fireworks. But the anniversary occurred unnoted.

First, the fact: in 1835, 150 years ago, the Baltimore & Ohio Railroad completed its branch line -- yes, its branch line -- between Baltimore and Washington. Now, the significance: the branch forever ended the isolation of Washington City, as the capital was known, from the rest of the nation, especially from New York and New England.

It's hard to appreciate, but in those days fewer than 100 people a day passed back and forth by horse-drawn stagecoach between Washington and Baltimore. And the railroad company, when considering construction, reckoned its possible profit not so much on growth but on how many of those coach riders it could divert.

Building the B&O's branch was considered a diversion from the investors' main (and ultimately achieved) purpose of building a railroad to tap the Ohio River valley and channel its freight into the port of Baltimore. But, in conjunction with other rail lines, the Washington branch developed into an important source of traffic in the early years. (For Washington-bound travelers, changing trains in Philadelphia was regarded with horror.)

Building the Washington branch entailed one of the finest bits of railroad architecture that still stands: Benjamin H. Latrobe's 700-foot curving stone viaduct across the Patapsco River south of Baltimore, at a place now called Relay. Designed for tiny peanut-whistle locomotives of 1835, it carries today's heavy diesel engines.

Let's pick up the words of B&O historian Edward Hungerford: "It is the 25th day of August 1835, and a warm summer sun already is shining . . . . Nearly a thousand folk come to ride [from Baltimore] . . . 16 cars are not going to be enough [so more are ordered] . . . . "

The train came to the Washington station, on what is now the Capitol grounds near the Taft Memorial, disgorged passengers for bibulous feasting at hotels, then took them home.

A 40-mile train line alone didn't end Washington's isolation, but it was the beginning. A rival and ultimately dominant railroad, today's Amtrak, began running trains to Washington in 1872.

The growth of the nation's railroad network, for a time of its steamboat network, then of its road network and finally of its airline network, brought the nation and its capital together -- and ended suggestions that the capital be moved to the geographic center of the country.

But we suspect that if the B&O were still a Baltimore-based corporation instead of being part of something called the CSX Corp., this sesquicentennial of trains into Washington would have been observed. Absentee conglomerates aren't very sentimental.