The ampersand can be traced back to the 1st century A.D. and the Old Roman cursive, in which the letters E and T occasionally were written together to form a ligature. In the later and more flowing New Roman Cursive, ligatures of all kinds were extremely common; figures 2 and 3 from the middle of 4th century are both examples of how the et-ligature could look in this script. During the following development of the Latin script that led up to the Carolingian minuscule (9th century) the use of ligatures in general diminished. The et-ligature, however, continued to be used and gradually became more stylized and less revealing of its origin.
Pearl, it's that figure on your keyboard above the number 7. We use it in place of the word "and." For example: You & I answered the same question. The ampersand in the above statement is: &
The best story I heard, and I believe it to be the true story, is about the method of teaching English schoolboys their tables and alphabet. They would "sing" them. We still did it when I was at school
When "singing" the alphabet they would recite all 26 letters and finish with "and per se and" recognising the abbreviation as a letter in its own right. The "and per se and" was contracted into ampersand, and it stuck.