Plovdiv in the context of "Upper Thracian Plain"

Bulgaria, officially the Republic of Bulgaria, is a country in Southeast Europe. It is situated on the eastern portion of the Balkans directly south of the Danube river and west of the Black Sea. Bulgaria is bordered by Greece and Turkey to the south, Serbia and North Macedonia to the west, and Romania to the north. It covers a territory of 110,994 square kilometres (42,855 sq mi) and is the tenth largest within the European Union and the sixteenth-largest country in Europe by area. Sofia is the nation's capital and largest city; other major cities include Burgas, Plovdiv, and Varna.

One of the earliest societies in the lands of modern-day Bulgaria was the Karanovo culture (6,500 BC). In the 6th to 3rd century BC, the region was a battleground for ancient Thracians, Persians, Celts, and Macedonians; stability came when the Roman Empire conquered the region in AD 45. After the Roman state splintered, tribal invasions in the region resumed. Around the 6th century, these territories were settled by the early Slavs. The Bulgars, led by Asparuh, attacked from the lands of Old Great Bulgaria and permanently invaded the Balkans in the late 7th century. They established the First Bulgarian Empire, victoriously recognised by treaty in 681 AD by the Byzantine Empire. It dominated most of the Balkans and significantly influenced Slavic cultures by developing the Cyrillic script. Under the rule of the Krum's dynasty, the country rose to the status of a mighty empire and great power. The First Bulgarian Empire lasted until the early 11th century, when Byzantine emperor Basil II conquered and dismantled it. A successful Bulgarian revolt in 1185 established a Second Bulgarian Empire, which reached its apex under Ivan Asen II (1218–1241). After numerous exhausting wars and feudal strife, the empire disintegrated and in 1396 fell under Ottoman rule for nearly five centuries.

Under the reign of Philip II (359–336 BC), the ancient kingdom of Macedonia, initially at the periphery of classical Greek affairs, came to dominate Ancient Greece in the span of less than 25 years, largely thanks to the character and policies of its king. In addition to utilising effective diplomacy and marriage alliances to achieve his political aims, Philip II was responsible for reforming the ancient Macedonian army into an effective fighting force. The Macedonian phalanx became the hallmark of the Macedonian army during his reign and the subsequent Hellenistic period. His army and engineers also made extensive use of siege engines. Chief among Philip's Thracian enemies was the ruler Kersebleptes, who may have coordinated a temporary alliance with Athens. In a series of campaigns stretching from 356 to 340 BC, Philip II managed to ultimately subjugate Kersebleptes as a tributary vassal, conquering much of Thrace in the process. Philip II also fought against the Illyrian king Bardylis, who threatened Macedonia proper, and against Grabos II and Pleuratus in Illyria (centred in modern-day Albania). In his newly conquered territories, he founded new cities such as Philippi, Philippopolis (modern Plovdiv, Bulgaria), Herakleia Sintike (Pirin Macedonia, Bulgaria), and Herakleia Lynkestis (modern Bitola, North Macedonia).

Philip II eventually campaigned against the city-state of Athens and her allies in the Aegean region, as well as Thebes after the decline of its hegemony in mainland Greece. In the defence of the Amphictyonic League of Delphi and in conjunction with the Thessalian League, Macedonia became a key player in the Third Sacred War (356–346 BC), defeating the Phocians, commanded by Onomarchus, at the Battle of Crocus Field in 352 BC. While poised to launch a direct assault on Athens in 346 BC, the Macedonian king was met with an Athenian embassy that arranged the Peace of Philocrates. As a result, Macedonia and Athens became allies, yet Athens was forced to relinquish its claims to the city of Amphipolis (in modern-day Central Macedonia).

Burgas (Bulgarian: Бургас, pronounced [burˈɡas] ), sometimes transliterated as Bourgas, is the second largest city on the Bulgarian Black Sea Coast in the region of Northern Thrace and the fourth-largest city in Bulgaria after Sofia, Plovdiv, and Varna, with a population of 210,646 inhabitants, while 226,137 live in its urban area. It is the capital of Burgas Province and an important industrial, transport, cultural and tourist centre.

The city is surrounded by the Burgas Lakes and located at the westernmost point of the Black Sea, at the large Burgas Bay. LUKOIL Neftochim Burgas is the largest oil refinery in southeastern Europe and the largest industrial enterprise. The Port of Burgas is the second largest port in Bulgaria, and Burgas Airport is the second most important in the country. Burgas is the centre of the Bulgarian fishing and fish processing industry.

Philippopolis (Ancient Greek: Φιλιππούπολις, Φιλιππόπολις) is one of the names of the ancient city (amongst which are Thracian Eumolpia/Pulpudeva, Roman Trimontium) situated where Plovdiv is today. The city became one of the largest and most important in the region and was called "the largest and most beautiful of all cities" by Lucian. During most of its recorded history, the city was known by the name Philippopolis (Ancient Greek: Φιλιππούπολις, romanized: Philippoúpolis, lit. 'Philip's city') after Philip II of Macedon. Philippopolis became part of the Roman Empire and capital of the Roman province of Thracia. According to Ammianus Marcellinus, Philippopolis had a population of 100,000 in the Roman period.

Philippopolis was in a fertile region on the banks of the Maritsa River (the ancient Hebrus). The city historically developed on seven syenite hills, some of which are 250 metres (820 feet) high, because of which Plovdiv is often referred to in Bulgaria as "The City of the Seven Hills".

The Maritsa, known in Greek as the Hebros and in Turkish as the Meriç, is a river that runs through the Balkans in Southeast Europe. With a length of 480 km (300 mi), it is the longest river that runs solely in the interior of the Balkan peninsula, and one of the largest in Europe by discharge. It flows through Bulgaria in its upper and middle reaches, while its lower course forms part of the border between Greece and Turkey. Its drainage area is about 53,000 km (20,000 sq mi), of which 66.2% is in Bulgaria, 27.5% in Turkey, and 6.3% in Greece. It is the main river of the historical region of Thrace, most of which lies in its drainage basin.

It has its origin in the Rila Mountains in Western Bulgaria, its source being the Marichini Lakes. The Maritsa flows east-southeast between the Balkan and Rhodope Mountains, past Plovdiv and Dimitrovgrad in Bulgaria to Edirne in Turkey. East of Svilengrad, Bulgaria, the river flows eastwards, forming the border between Bulgaria (on the north bank) and Greece (on the south bank), and then between Turkey and Greece. At Edirne, the river meets its two chief tributaries Tundzha and Arda, and flows through Turkish territory on both banks. It then turns towards the south and forms the border between Greece on the west bank and Turkey on the east bank all the way to the Aegean Sea, which it enters near Enez, forming a river delta. The upper Maritsa valley is a principal east–west route in Bulgaria. The unnavigable river is used for hydroelectric power generation and for irrigation.

The Eyalet of Rumeli, or Eyalet of Rumelia (Ottoman Turkish: ایالت روم ایلی, romanized: Eyālet-i Rūm-ėli), known as the Beylerbeylik of Rumeli until 1591, was a first-level province (beylerbeylik or eyalet) of the Ottoman Empire encompassing most of the Balkans ("Rumelia"). For most of its history, it was the largest and most important province of the Empire, containing key cities such as Edirne, Yanina (Ioannina), Sofia, Filibe (Plovdiv), Manastır/Monastir (Bitola), Üsküp (Skopje), and the major seaport of Selânik/Salonica (Thessaloniki). It was also among the oldest Ottoman eyalets, lasting more than 500 years with several territorial restructurings over the long course of its existence.

The capital was in Adrianople (Edirne), Sofia, and finally Monastir (Bitola). Its reported area in an 1862 almanac was 48,119 square miles (124,630 km).

Northern Thrace or North Thrace (Bulgarian: Северна Тракия, Severna Trakiya; Turkish: Kuzey Trakya; Greek: Βόρεια Θράκη), also called Bulgarian Thrace, constitutes the northern and largest part of the historical region of Thrace. It is located in Southern Bulgaria and includes the territory south of the Balkan Mountains and east of the Mesta River, bordering Western Thrace and East Thrace in the south, and the Black Sea in the east. It encompasses Sredna Gora, the Upper Thracian Plain, and 90% of the Rhodopes.

The climate ranges from subtropical to transitional continental and mountainous. The highest temperature recorded in Bulgaria occurred here: it was 45.2 °C (113.4 °F; 318.3 K) at Sadovo in 1916. The main rivers of the region are the Maritsa and its tributaries. Notable cities include Plovdiv, Burgas, Stara Zagora, Sliven, Haskovo, Yambol, Pazardzhik, Asenovgrad, Kardzhali, Dimitrovgrad, Kazanlak and Smolyan. Northern Thrace has an area of 42,073 km.