Complex sentence: Though the city over the century had grown around the River Liffey, its buildings as in many other medieval centres backed onto the river, often allowing for the dumping of household waste directly into the river, it being a form of collective sewer.
Split into simpler sentences: Though the city over the century had grown around the River Liffey, as in many other medieval cities, buildings backed onto the river. This allowed the dumping of household waste directly into the river, creating a form of collective sewer.