BASH: multiple variable substitution

a=1;
x=a;

echo ${$x}

bash: ${$x}: bad substitution

eval y='$'$x;echo $y

1

echo a=$(eval echo '$'$(echo $x))

a=1

a0=000
a1=111
for i in 0 1 ; do echo a$i=$(eval echo '$'$(echo a$i));done

a0=000
a1=111