Parvin E'tesami, Sadegh Hedayat, and Simin Daneshvar, among others. Not all Persian literature is written in Persian, as works written by Persians in other languages—such as Arabic and Greek—might also be included. At the same time, not all literature written in Persian is written by ethnic Persians or Iranians, as Turkic, Caucasian, and Indic authors have also used Persian literature in the environment of Persianate cultures. Architecture The most notable examples of ancient Persian architecture are the works of the Achaemenids hailing from Persis. Achaemenid architecture, dating from the expansion of the empire around 550 BC, flourished in a period of artistic growth that left a legacy ranging from Cyrus the Great's solemn tomb at Pasargadae to the structures at Persepolis and Naqsh-e Rostam. The Bam Citadel, a massive structure at constructed on the Silk Road in Bam, is from around the 5th century BC. The quintessential feature of Achaemenid architecture was its eclectic nature, with elements from Median architecture, Assyrian architecture, and Asiatic Greek architecture all incorporated. The architectural heritage of the Sasanian Empire includes, among others, castle fortifications such as the Fortifications of Derbent (located in North Caucasus, now part of Russia), the Rudkhan Castle and the Shapur-Khwast Castle, palaces such as the Palace of Ardashir and the Sarvestan Palace, bridges such as the Shahrestan Bridge and the Shapuri Bridge, the Archway of Ctesiphon, and the reliefs at Taq-e Bostan. Architectural elements from the time of Iran's ancient Persian empires have been adopted and incorporated in later period. They were used especially during the modernization of Iran under the reign of the Pahlavi dynasty to contribute to the characterization of the modern country with its ancient history. Gardens Xenophon, in his Oeconomicus, states: The Persian garden, the earliest examples of which were found throughout the Achaemenid Empire, has an integral position in Persian architecture. Gardens assumed an important place for the Achaemenid monarchs, and utilized the advanced Achaemenid knowledge of water technologies, including aqueducts, earliest recorded gravity-fed water rills, and basins arranged in a geometric system. The enclosure of this symmetrically arranged planting and irrigation by an infrastructure such as a palace created the impression of "paradise". The word paradise itself originates from Avestan (Old Persian ; New Persian , ), which literally translates to "walled-around". Characterized by its quadripartite (čārbāq) design, the Persian garden was evolved and developed into various forms throughout history, and was also adopted