Russian-Iranian relations over the centuries and in recent decades have been complex and elastic. They have been simultaneously good in some areas while bad in others. Even at their worst, they have been able to stretch without breaking. A visitor to the Kremlin Armory can admire the 89-carat diamond that the Shah of Persia sent to Nicholas I to assuage the murder by a Tehran mob in 1829 of Russian Ambassador Alexander Griboyedov and his staff. The spectacular gift was part of a package deal to which both sides contributed to put the ugly incident behind them. More recently, Moscow greatly angered Tehran in 2010 when it broke the contract for the S-300 (U.S./North Atlantic Treaty Organization [NATO]-designated SA-20) long-range air defense missile system, yet the two countries have subsequently worked hard for a semblance of continued engagement.