"Baltimore used to be in the days of Slavery one of the most difficult
places in the South for even free colored people to get away from, much
more slaves. The rule forbade any colored person leaving there by rail
road or steamboat, without such applicant had been weighed, measured, and
then given a bond signed by unquestionable signatures well known. Baltimore
was rigid in the extreme, and was a never-failing source of annoyance,
trouble and expense to colored people generally, and not unfrequently to
slave-holders too, when they were traveling North with "colored servants'"...But,
not withstanding all this weighing, measuring and requiring of bonds, many
travelers by the Underground Rail Road took passage from Baltimore."
-- from William Still, 1872
A detailed study of Baltimore City is forthcoming.