1520-Hernán Cortés and the Tlaxcalans defeat a numerically superior Aztec force in the Battle of Otumba in Mexico1807-French Emperor Napoléon Bonaparte and Russian Tsar Alexander I meet on a raft in the middle of the Neman River and sign the first Treaty of Tilsit1937-Japanese and Chinese troops clash at the Marco Polo Bridge near Beijing, beginning the Second Sino-Japanese War1947-Alleged and disputed Roswell, New Mexico UFO incident2005-Coordinated terrorist bomb blasts strike London's public transport system during the morning rush hour, killing 52 and injuring 7002005-Influenced by global Live 8 concerts, G8 leaders pledge to double 2004 levels of aid to Africa from $25 billion to $50 billion by the year 2010 and to drop the debt owed by 18 of the most heavily indebted poor countries. Results are mixed.