Add 5 black tea bags and 2 cups of boiling water to a teapot and let steep, covered, for two hours.
While the tea is steeping, make a date syrup by adding the dates and 4 cups of cold water to a pot on the stove.
Bring the date/water mixture to a boil, then continue to boil for 25 minutes.
Using a strainer, pour the date syrup out of the pot and reserve it (you can either discard the dates or store them in an airtight container in the fridge for a few days and use them to sweeten smoothies).
Allow the date syrup to cool.
After the tea has finished steeping, add the tea, date syrup, and 4 cups of cold water to a large pitcher.
Refrigerate for at least 2 hours.
Serve by filling glasses with ice cubes, a lemon slice or two, then fill the glass with the sweet tea mixture.