Sorry, I couldn't find pricing data for that day. The closing price for the S&P 500 (GSPC) on September 10, 2001 was $1,092.54. It was up 0.6% for the day. The latest price is $6,723.29.
DATE
OPEN
HIGH
LOW
CLOSE
VOLUME
September 10 2001
$1,085.78
$1,096.94
$1,073.15
$1,092.54
1,276,600,000
Daily pricing data for the S&P 500 dates back to 12/30/1927, and may be incomplete.