 Federal Hill's views were first put to commercial use in 1795 when, in cooperation with the Maritime Exchange, Captain David Porter established a "marine observatory" and signal tower on the site.The tower provided a panorama that stretched a good 15 miles or more down the Patapsco River.Spotting an incoming ship, the watchman would unfurl the observatory's "house flag" to alert the merchants and ship owners at the Maritime Exchange of an imminent arrival.