Context:: Architecture of a software system represents the key design decisions and therefore its quality plays an important role to keep the software maintainable. Code smells are indicators of quality issues in a software system and are classified based on their granularity, scope, and impact. Despite a plethora of existing work on smells, a detailed exploration of architecture smells, their characteristics, and their relationships with smells in other granularities is missing. Objective:: The paper aims to study architecture smells characteristics, investigate correlation, collocation, and causation relationships between architecture and design smells. Method:: We implement smell detection support for seven architecture smells. We mine 3 073 open-source repositories containing more than 118 million lines of C# code and empirically investigate the relationships between seven architecture and 19 design smells. Results:: We find that smell density does not depend on repository size. Cumulatively, architecture smells are highly correlated with design smells. Our collocation analysis finds that the majority of design and architecture smell pairs do not exhibit collocation. Finally, our causality analysis reveals that design smells cause architecture smells.