Incense trade route in the context of "Incense"

Petra (Arabic: ٱلْبَتْراء‎, romanized: Al-Batrāʾ; Ancient Greek: Πέτρα, lit. 'Rock'), originally known to its inhabitants as Raqmu (Nabataean Aramaic: 𐢛𐢚𐢒‎ or 𐢛𐢚𐢓𐢈‎, *Raqēmō), is an ancient city and archaeological site in southern Jordan. Famous for its rock-cut architecture and water conduit systems, Petra is also called the "Rose City" because of the colour of the sandstone from which it is carved. The city is one of the New 7 Wonders of the World and a UNESCO World Heritage Site.

The area around Petra has been inhabited from as early as 7000 BC, and was settled by the Nabataeans, a nomadic Arab people, in the 4th century BC. Petra would later become the capital city of the Nabataean Kingdom in the second century BC. The Nabataeans invested in Petra's proximity to the incense trade routes by establishing it as a major regional trading hub, which gained them considerable revenue. Unlike their enemies, the Nabataeans were accustomed to living in the barren deserts and thus were able to defend their kingdom. They were particularly skillful in agriculture, stone carving, and rainwater harvesting.

Najran (Arabic: نجران Najrān; IPA: [nad͡ʒ.raːn]), is a city in southwestern Saudi Arabia. It is the capital of Najran Province. Today, the city of Najran is one of the fastest-growing cities in the kingdom of Saudi Arabia. As of the 2022 census, the city population was 381,431, with the population of the governorate of Najran being 592,300. Today, the population is primarily Ismaili with a Sunni minority.

The ancient city of Najran is now largely in ruins, the archaeological site Al-Okhdood, located south-east of the present-day city. In ancient times, this Najran was a major urban, agriculture, industrial (cloth, leather), and trade (incense) center, located in the midst of a fertile wadi (valley), called the Wadi Najran. Najran was also located at the intersection of two main caravan routes: one running from Hadhramaut, to the Hejaz, to the Eastern Mediterranean, and another running from the northeast through Al-Yamama and into Mesopotamia. Its pre-Islamic history is notable for its Christian community, including its central role in South Arabian Christianity and the massacre of this community by the king Dhu Nuwas.

The influence of ancient Rome in the Arabian Peninsula took root through extensive commerce between Arabs and Romans, who frequently traded with each other on the incense route and the spice route. The Romans knew of Arabia in three roughly divided regions: Arabia Petraea (lit. 'Rocky Arabia'), Arabia Deserta (lit. 'Deserted Arabia'), and Arabia Felix (lit. 'Fertile Arabia'). Collectively, they were a natural stop on the Roman trade route with India, especially by way of the Red Sea. While the Roman Republic had held territory in the Levant, it was not until the time of the Roman Empire that parts of Arabia proper came under Roman rule.

Arabia Petraea was a Roman province that was established after the Roman conquest of the Nabataean Kingdom in 106, consisting of the Sinai Peninsula and parts of the Southern Levant. Arabia Deserta referred to the uncontrolled and sparsely populated interior of the Arabian Peninsula, namely the vast Arabian Desert, which was inhabited by various Arab tribes. Arabia Felix, referring to South Arabia, was home to many independent Arab kingdoms, which variously traded with or fought wars against the Romans.

al-Ula (Arabic: ٱلْعُلَا‎, romanized: al-ʿUlā), officially AlUla, is an ancient Arabian oasis city and governorate located in Medina Province, Saudi Arabia, 350 kilometres (220 miles) northwest of the city of Medina. Situated in the Hejaz, a region that features prominently in the history of Islam as well as several pre-Islamic Semitic civilizations, al-Ula was a market city on the historic incense trade route that linked India and the Persian Gulf to the Levant and Europe.

From an archaeological perspective, the immediate vicinity contains a unique concentration of precious artifacts, including well-preserved ancient stone inscriptions that illustrate the development of the Arabic language, and a concentration of rock dwellings and tombs that date from the Nabatean and Dedanite periods that coincided with Greco-Roman influence during classical antiquity. Saudi Arabia's first UNESCO World Heritage Site, Hegra (also known as al-Hijr, or Mada'in Ṣalih), is located 22 km (14 miles) north of the city, in al-Ula governorate. Built more than 2,000 years ago by the Nabataeans, Hegra is often compared with its sister city of Petra, in Jordan. Meanwhile, the ancient walled oasis city of al-Ula, locally known as al-Dirah, situated near the oasis's palm grove that allowed for its settlement, contains a dense cluster of mudbrick and stone houses. al-Ula was also the capital of the ancient Lihyanites (Dedanites).

Citrus is a genus of flowering trees and shrubs in the family Rutaceae. Plants in the genus produce citrus fruits, such as citrons, mandarins, and pomelos. Many important citrus crops have been developed through extensive hybridization, including oranges, lemons, grapefruits, and limes, all of which have many cultivars.

Citrus is native to South Asia, East Asia, Southeast Asia, Melanesia, and Australia. Indigenous people in these areas have used and domesticated various species since ancient times. Its cultivation first spread into Micronesia and Polynesia through the Austronesian expansion (c. 3000–1500 BCE). Later, it was spread to the Middle East and the Mediterranean (c. 1200 BCE) via the incense trade route, and then from Europe to the Americas.