# Why choose a Dirichlet distribution in Latent Dirichlet Allocation (LDA)?

I am studying Latent Dirichlet Allocation (LDA), but I don't have much knowledge of stochastic processes.

From Wikipedia:

LDA assumes the following generative process for a corpus $$D$$ consisting of $$M$$ documents each of length $$N_{i}$$:

1. Choose $$\theta _{i}\sim \operatorname {Dir} (\alpha )$$, where $$i\in \{1,\dots ,M\}$$ and $$\mathrm {Dir} (\alpha )$$ is a Dirichlet distribution with a symmetric parameter $$\alpha$$

My question is this: why Dirichlet distribution? Are there any particular properties of this distribution that make it suitable for this model?