The Garden of Fronteira is situated on the slope of Park of Monsanto, a forest park located West of Lisbon.
The Park of Monsanto is located mostly on the basaltic mantle of the Mafra-Lisbon Volcanic Complex and is still composed of other surrounding formations, namely calcareous. With about 900ha this is an area of old human occupation with prehistoric vestiges. Planting began in the decade of 1930 on extensive areas of intense cereal cultivation. During nine decades it has undergone successive plantations and today it presents a dense forest in which dominate extensive areas of umbrella pine (Pinus pinea) and pine of alepo (Pinus halepensis), Cupressus spp. Eucaliptus globulus Labill., Acacia spp, Quercus faginea L., Quercus suber L. x Quercus rotundifolia L. and Olea europaea L..

The Garden was built during the years 1668-1670 by the 1st Marquis of Fronteira, as a celebration of the victory of the Portuguese armies against Spain, in the wars of Restoration of Independence (1640-1668). Dom João de Mascarenhas, who commissioned the garden, became the 1st Marquis of Fronteira as a reward of his distinguished participation in these wars. The iconographical program of the garden is a celebration of both events. Portuguese independence is celebrated through the inclusion of a gallery with the busts of Portuguese kings. The attribution of the title to the Marquis is alluded through the statue of the allegory of Occasio (Opportunity). The exuberant decoration in panels of tiles (azulejos) alluding to the role of the nobility as the support of kings, as well as to the renewal of court life after the war, contribute to the richness of a decorative program allusive to war and peace, as well as to the exaltation of Portuguese monarchy and identity.

This historical garden is composed of a formal garden with a classical parterre with geometrical flowerbeds bordered with boxwood. The formal garden has a large Basin called the Knights Pond on the south. It is surrounded by walls decorated with panels of tiles representing the 12 months of the year (East) the 12 signs of the Zodiac (North) and the four elements, planets and constellations (West). In contrast to what happened in the city of Lisbon, water was abundant here, and the garden takes advantage of it by displaying this richness in five fountains situated at the centre of the formal garden, at the centre of each large flowerbed as well as in the large basin. The wall of the basin displays 14 panels of tiles depicting noblemen. Above the wall is placed the gallery of Kings, with the busts of the Portuguese Kings. Through a staircase one can accede to a second garden, known as the Garden of Venus, due to the fountain with a statue of this goddess placed at its centre. At the very end of this “intimate” garden is placed a garden grotto known as “Casa do Fresco” richly decorated with tiles and rocaille. In front of this grotto there is the celebrated basin of the SS, a pond in wavelike form decorated with infants and dolphins. There are interesting water jets inside and outside the grotto. During the eighteenth century some exotic trees have been added to this garden. On an inferior level, facing “Casa do Fresco” one can find yet another fountain richly decorated with rocaille, with three water mouths, known as the “Fonte da Carranquinha”.

From the correspondence exchanged beteen the 1st Marquis of Fronteira and the Kings ambassador in Paris, it can be deduced that the garden was designed at the end of the 1660’s, when the Marquis asked for an experienced French master gardener to be send to Lisbon. In 1669 when Cosimo di Medici visited the Palace the works in the garden were already quite advanced. It must have been near completion by 1670, when it was solemnly inagurated in the presence of the King Regent Pedro II of Braganza. It was built as a recreational site, for the palace was a secondary residence used mostly for hunting and summer vacation.
The garden seems to have suffered only small scale damages during the Lisbon earthquake of 1755. These damages attained mostly the South Wall and part of the Garden of Venus. The four busts of Eighteenth Century kings situated in the Wall of this garden were added during the reconstruction made in the eighteenth century by the 5th Marquis of Fronteira, with whom the palace became the main residence of the family.

The Garden is part of the architectural complex known as Palácio Fronteira, which includes a 17th century palace and a wood. Visitors can visit the interiors of the palace through guided tours. The palace, which is still inhabited by the descendants of the Mascarenhas family is richly decorated and completely furnished with historical and precious objects from the sixteenth, seventeenth, eighteenth and nineteenth centuries. Since several members of the familiy have been Vice Roys in India, and in Brazil, there are interesting collections of objects from Eastern and South American cultures.