Even more than for cross-cultural trade and biological diffusions, it has proved difficult to study cultural encounters and exchanges on large scales, partly because scholars lack a common vocabulary or set of conceptual tools for comparative cultural analysis. Yet Mary W. Helms has probed the political and cultural significance of long-distance travel, and I have argued in my own work that despite local differences, several patterns of cross-cultural conversion, conflict, and compromise are recognizable over the long term.26 Further explorations of large-scale cultural interactions would make welcome additions to scholarship in world history.