Just as Austria, Portugal is a small country, but while Austria was much bigger before the Great War, Portugal was always of its current size.
What Portugal had and Austria direly lacked (at least if we disregard the short episode of the reign of Charles V), that were colonies. Colonies were the wealth of Portugal, colonies were what it clung to, almost to a bitter end, and that wealth is the reason for the unusual number of oversized imperial buildings in and around Lisbon.
Not everything was finished though, at least not always in time (as we already saw in Santa Engrácia), and in some cases a half-finished building is what we see today. One example for that is the Palácio Nacional da Ajuda. I didn’t go in, I just went through its courtyard on my way to Belém.