Complex sentence: When Annapolis, Maryland was established as a city at the beginning of the 18th century, the streets were established in circles, which encouraged the creation of shortcuts, which over time became paved alleys.
Split into simpler sentences: When Annapolis, Maryland, was established as a city at the beginning of the 18th century, the streets were established in circles. That encouraged the creation of shortcuts, which over time became paved alleys.