Baltimore is located at the head of the Patapsco River estuary, 15 miles (or 24 kilometers) above Chesapeake Bay.  Baltimore is Maryland's largest city and economic hub.  It was established in 1729, named after the Irish barony of Baltimore, which was the seat of the Calvert family, the proprietors of the colony of Maryland).  It ibecame the first U.S. Roman Catholic diocese in 1789.  In 1827 the nation's first railroad began operations there.  In World War One, Baltimore began to develope industrially, and it has since became a major sea port.