By the beginning of the 18th century, life in the city of Edinburgh (today's Old Town) was overcrowded and unsanitary.
Edinburgh was not a good place to live in the 1700s. 
mnli hypothesis: Edinburgh was not a good place to live in the 1700s.  premise: By the beginning of the 18th century, life in the city of Edinburgh (today's Old Town) was overcrowded and unsanitary.