The heart of the city is Viejo Madrid, Old Madrid, a largely 16th-century city built upon the layout of narrow, winding streets of an old Moorish settlement.
Parts of Old Madrid date back to earlier than the 16th century. 
mnli hypothesis: Parts of Old Madrid date back to earlier than the 16th century.  premise: The heart of the city is Viejo Madrid, Old Madrid, a largely 16th-century city built upon the layout of narrow, winding streets of an old Moorish settlement.