At this point, the vast majority of passengers who had boarded lifeboats were from first- and second-class. Few third-class (steerage) passengers had made it up onto the deck, and most were still lost in the maze of corridors or trapped behind gates and partitions that segregated the accommodation for the steerage passengers from the first- and second-class areas. This segregation was not simply for social reasons, but was a requirement of United States immigration laws, which mandated that third-class passengers be segregated to control immigration and to prevent the spread of infectious diseases. First- and second-class passengers on transatlantic liners disembarked at the main piers on Manhattan Island, but steerage passengers had to go through health checks and processing at Ellis Island. In at least some places, "Titanic"s crew appear to have actively hindered the steerage passengers' escape. Some of the gates were locked and guarded by crew members, apparently to prevent the steerage passengers from rushing the lifeboats. Irish survivor Margaret Murphy wrote in May 1912: