It is often useful to build matrices out of smaller matrices.
Horizontal Concatenation
Matrices (and vectors, which are treated as column vectors) can be horizontally concatenated using the hcat function.
julia> hcat([1 2; 3 4], [5 6 7; 8 9 10], [11, 12])
2×6 Array{Int64,2}:
1 2 5 6 7 ...