Christie's is offering a brooch once owned by Catherine II of Russia, the powerful 18th-century monarch known for her taste in art and jewelry. The 60-to-70 carat emerald was a gift to Sophie Dorothea when she wed Catherine's son Tsar Paul I in 1776.

The hexagonal cut Colombian emerald is surrounded by rose and old mine-cut diamonds set in silver-topped gold. It is estimated to sell for $1 million to $1.5 million.