Complex sentence: Poverty was not uncommon among the residents of the Forest of Pendle, hence the building was likely to have been no more than a hovel, and "tower" may therefore have been a sarcastic name given by local residents.
Split into simpler sentences: Poverty was not uncommon among the residents of the Forest of Pendle, hence the building was likely to have been no more than a hovel. "Tower" may therefore have been a sarcastic name given by local residents.