How to change value of sub-rectangle in large array

I have a 1200x1200 array of zeros and I want most of them to be zeros, but I want to insert rectangles (or circles) of 1's at certain positions. For example I want a 20x20 rectangle of 1's starting at position (621,499). Is there an easy way to do this without typing in each cell value?

i.e. I do not want to use A(x,y)=1 for a repetitive amount of times. I know I could use a for loop, but I prefer not to. Please help!

Answer 1

[Walter Roberson]

Matrix(621:621+20-1, 499:499+20=1) = 1;