Simplify the following text for a Grade 11 native English-speaking person.
Original: To the surprise of the men garrisoned in the Alamo , on February 23 , a Mexican army , led by General Antonio Lopez de Santa Anna , arrived .
Simplified: On February 23 , a Mexican army , led by General Antonio LÃ pez de Santa Anna , showed up , and the Mexican army surrounded the Alamo , ready to take it over .