The Monumental Door is a mixture of the triumphal arch and a fortified gateway, signposting the entranceway to the tunnel that leads to the residential wings and the Palace of Pena reception rooms, which, being more private, were set in a better “protected” and secluded corner. Its architectonic composition contains references to the most emblematic buildings in Lisbon from the Era of Discoveries and the Manueline period, such as Casa dos Bicos (House of the Spikes) through to the diamond points in a chequered pattern as well as the Tower of Belém through the two cylindrical bartizans with twinned cupolas, resting on lion’s heads (feasibly representing a lion and a lioness). Similarly, the Cunhal das Bolas in Lisbon’s Bairro Alto neighborhood served as the model for the spheres in relief around the arch (the same solution was adopted for the opening access to the Round Path and, as with the tunnel, represents a military architectural feature). The perfectly aligned archway rests upon depictions of serpents with the foundation stone sculpted into a great medieval helm. On the upper turrets, the lateral merlons display animal skins from which hang Crosses of Christ while the central merlon features two overlaying swords in an allusion to the knightly character of the Palace of Pena. Behind the Monumental Door was the Drawbridge, which formed an obligatory feature to the defensive systems of Central European medieval castles from which Baron von Eschwege took his inspiration for the Castle of Pena project as the Palace was known at the time of its construction.