Tradition of worshiping Lord Shiva in Mithila
Parthiva Shivalinga Puja (Devanagari: पार्थिव शिवलिंग पुजा, Romanised: "Pārthiva Śivaliṅga Pūjā") is a popular tradition of worshiping Lord Shiva in the Mithila region of the Indian Subcontinent. In this tradition, devotee worships Shivalingas made by mud. The mud Shivalingas are worshipped either individually at home or at public place by large groups of devotees.
Etymology.
Parthiva Shivlinga Puja is a group of three Indic words Parthiva, Shivlinga and Puja. The literal meaning of "Parthiva" is earthly i.e., made from earthly material like soil, sand or mud. Similarly "Shivalinga" is the iconic representation of Lord Shiva and "Puja" literally means worship. Therefore, the literal meaning of Parthiva Shivlinga Puja is the worship of Shivlinga made by soil, sand or mud.
Description.
The tradition of the Parthiva Shivalinga Puja originated in the Hindu text Shiva Purana. According to the text Shiva Purana, the Parthiva Shivalingas should be made from the soil of a holy river or pond. In the text Shiva Purana, when sages asked about the greatness of the Parthiva Shivalingas to Suta, then he explained the greatness of the worship of the Parthiva Shivalingas. Suta told that Parthiva Shivalinga is the best form of Lord Shiva among his eight cosmic bodies. He further said that Brahmins, Lord Vishnu, Prajapati and other sages had achieved the great things they had desired by worshipping the Parthiva Shivalingas. Similarly Devatas, Asuras, Gandharvas and many men had achieved greatness by worshipping it. In Kali Yuga, the Parthiva Shivalinga is the most auspicious form of Lord Shiva to worship. It is said that in Kali Yuga, the sage "Mandapa" started the worship of "Parthiva Shivlinga". The sage Mandapa was the son of the sage "Kushmanda". Since the tradition is originated from the text Shiva Purana, it could be followed by any Hindu adherents but it is less seen in other parts of the subcontinent. This tradition is still alive and popular among the Maithil communities in the Mithila region. In this region, Maithil Brahmins still follow the tradition of the Parthiva Shivalingas Puja in their homes while worshiping Lord Shiva. They also organise grand ceremonies of the Parthiva Shivalingas Puja at some big public grounds in the region on some auspicious day every year.
Similarly there is story in the "Mahatmya" of "Kedaareshwara" and "Bhimashankara" "Jyotirlinga" about the two avatars "Nara" and "Naaraayana" of Lord Vishnu who worshipped making Parthiva Shivalingas daily during their "Tapasyas" at "Badarikaashrama". 
In the Treta Yuga, Lord Rama worshipped Parthiva Shivalinga. In Ramayana, there is a reference of Lord Rama worshipping Parthiva Shivalinga on the bank of Indian Ocean at Rameshwaram. It is said that before attacking the King Ravana of Lanka, Lord Rama made a Parthiva Shivalinga with the sand on the ocean bank to worship Lord Shiva, so that he would be blessed by Lord Shiva for the victory on the King Ravana.
Recent notable observances in Mithila.
In the recent years, the devotees of Mithila region have organised some major grand celebration of the Parthiva Shivalingas Puja, which have been recorded as notable grand celebration in the region. These grand celebrations have created histories of the notable milestones for worshiping a very large numbers of the Parthiva Shivalingas by a very large numbers of devotees at some public places in the region. The first grand celebration of the Parthiva Shivalingas Puja was organised at the famous Barabigha ground in the city of Janakpur in the year 2017. In this grand celebration, around 3 crores 65 lakhs of Parthiva Shivalingas were made and worshiped by the devotees there.
The second grand celebration of the Parthiva Shivalingas Puja was organised at the Saurath Sabha Gachhi near the outskirts of the city of Madhubani in the year 2022. It said that around 3 crores 51 lakhs Parthiva Shivalingas were made and worshiped by the devotees there. In the campus of Saurath Sabha, there is also a Lord Shiva temple known as Madhaweshwar Nath Mahadev Mandir.
Similarly at the campus of "Mukteshwar Sthan Mandir" in the Devahar village of Madhubani district, a grand celebration of the Parthiva Shivalingas Puja was organised on 5 November 2023, in which around 1 crore 25 lakhs of Parthiva Shivalingas were made and worshiped by devotees. Same year in the december month, the fourth grand celebration of the Parthiva Shivalingas Puja was organised at Uchchaith village near Benipatti sub divisional town, in which 4 crores 51 lakhs Parthiva Shivalingas were made and worshiped by a large numbers of devotees.
On the occasion of "Akshay Navami" on 10 November 2024, the fifth grand Parthiva Shivalingas Puja was organised at the campus of "Dayal Baba Durga Mandir" in Koriyahi village of the Sitamarhi district in Mithila region. In this grand celebration, around 2 crores 91 lakhs of Parthiva Shivalingas were made and worshiped by the devotees participated in the celebration. In the celebration, Brahmins from different 101 villages of the Madhubani, Darbhanga and Sitamarhi districts including the Mithila region of Nepal participated for making and worshipping the Parthiva Shivalingas there.