Complex sentence: A 165-foot-high memorial was erected in Calcutta in his memory; however, Sir David Ochterlony's greatest legacy is the continuing recruitment of Gurkhas into the British and Indian armies.
Split into simpler sentences: A 165-foot-high memorial was erected in Calcutta in his memory. But Sir David Ochterlony's greatest legacy is the continuing recruitment of Gurkhas into the British and Indian armies.