The Medieval Period – [1100AD – 1500AD]
By late 12th century, the Indian classical music and dance in a combined form had evolved into a distinctive art form with a firm theoretical foundation contributed by eminent scholars from many regions of present day India. At this juncture there was not any distinction between Hindustani and Karnatic styles of music and it was just known as ‘Sangita’ (Music of India).
These developments took place during favorable times in the Indian sub-continent with rich patronage from various native kings and dynasties in power during those times. However, soon India was about to enter a new era of the Muslim kingdoms: – The ‘Sultanate of Delhi’ was established in 1206AD. Later on, Moghul invaders from foreign lands occupied the Indian subcontinent in 1526AD who ruled large swathes of present day northern and some parts of central India. Their kingdoms declined and perished towards 1707AD. From a cultural perspective these developments altered the course of natural evolution of native arts and culture. To a certain degree it impacted the vibrant academic atmosphere that was nurturing the evolution of native Indian classical music. However, in retrospect, as historical evidence shows, the impact did not majorly affect the enthusiasm of scholars – even though it may have altered the course of evolution of arts and music.
Another great treatise of early 12th century in the form of encyclopedia was the ‘Mānasollāsa’, also known as ‘Abhilashitartha Chintamani’. The Mānasollāsa encyclopedic treatise was written in Sanskrit in a Kannada language speaking region by the South Indian king Someshvara III of the Kalyani Chalukya dynasty. Organized as five books, among a multitude of topics, it extensively discusses arts with focus on music and dance.
It was also during this time Sarangadeva (1175AD–1247AD), the 13th-century Indian musicologist authored ‘Sangita Ratnakara’ – the classical Sanskrit text on music and drama. To this day, it is considered to be the authoritative treatise in Indian classical music by both the Hindustani music and the Karnatic music traditions.
Sarangadeva was born in a Brahmin family of Kashmir. In an era of Islamic invasion of the northwest regions of the Indian subcontinent and the start of Delhi Sultanate, his family migrated south and settled in the Hindu kingdom in the Deccan region ruled by the Yadava dynasty near Ellora Caves (Present day Maharashtra). 
Sarangadeva presented his ideas on music and dance in seven chapters of Sangita Ratnakara, but integrated it with philosophical context. He systematically presented his ideas on the nature of sound, register, the smallest distinct sounds that humans can hear and musical instruments can produce (shruti), musical scales and modes, 264 ragas, beats and role of time (tala), prosody (Chandas), relation between performance arts and human emotions and sentiments, musical and vocal ornaments, the composition of drama and songs, and the limitless opportunities available to the artist to express and affect her audience. 
To date, SarangaDeva’s Sangita Ratnakara is considered as a major mile stone in the evolution of music. Poet Jayadeva’s ‘Gita Govinda’ in the form of Ashtapadi was composed during this period. (1175-1200AD)
By this time, cultural influences from Persia and Arab had started influencing the evolution of Indian music in the northern part of India. Amir Khusro, a poet and musician under many Delhi Sultanate kings introduced Persian and Arabic elements to Indian music. He originated the ‘Khayal’ and ‘Tarana’ style of music which is now integral part of Hindustani music. A mild distinction was slowly building up in the overall style and practice of Indian music practiced in the northern part of India which eventually led to birth of what is known today as “Hindustani Sangita” while music in south of India came to be known as “Karnataka Sangita” relatively less influenced from outside cultures. The word Karnataka is a combination of ‘Karna’ (ears) and ‘ataka’ (pleasant) meaning that which is pleasant to hear.
In 1336AD, during a tumultuous period during which wars and invasions on neighboring kingdoms by Muslim kings to expand their territory was common, Sage Vidyaranya, a brilliant scholar, visionary, philosopher and a statesman, emerged on the scene as a powerful force who was the key architect in founding and establishing the ‘Vijayanagara Empire’. This empire, also known as ‘Karnata Rajya’ would eventually expand into most of southern and western regions of India. It successfully stemmed the advancement of Muslim invasions into southern India thereby shielding the native culture and traditions from the influences of Islamic culture. For the next 250 years, various emperors and kings under Vijayanagara empire and its successor kingdoms would provide unprecedented levels of patronage for the advancement of music and arts. It was during this period Thanjavur began to emerge as a seat of music.
Sage Vidyaranya also authored a music treatise called ‘Sangita Saara’ introducing new concepts to the music theory including the concept of ‘mela’.
Note: The term ‘mela’ was coined as an attempt to group and classify in some logical fashion the numerous musical scales (phrase based Ragaas) that had evolved by then. Mela was meant to be a parent scale under which musical scales confirming to a set of rules could be grouped under. Mela was still a theoretical concept and not an actual scale in practice.
Other iconic works during 14th and 15th century was ‘Sangitaraaja’ authored by Khumbha Maharana of Mewar and a commentary on Sangeeta Ratnakara authored by Kallinatha.
It was also during this time the Haridaasa movement was taking roots in the Kannada speaking regions (present day Karnataka) of the Vijayanagara Empire. It was primarily rooted in the ‘Bhakti’ concept. In this lineage was born sage Purandara Dasa who was a vaggeyakara (composer-performer), a lakshanakara (musicologist), and the founder of musical pedagogy. For all these reasons and the enormous influence that he had on present day Karnatic music, musicologists call him the “Sangeeta Pithamaha” (lit. grandfather) of Karnatic music. Purandara Dasa systematized the method of teaching Carnatic music which is followed to the present day. He introduced the raga Mayamalavagowla as the basic scale for music instruction and fashioned series of graded lessons such as Swaravalis, Janti-Swaras, Alankaras, Lakshana-Geetas, Prabandhas, Ugabhogas, Dhaatu-Varase, Geeta, Sooladis and Kritis. Another of his important contributions was the fusion of Bhaava, Raga, and Laya in his compositions . Purandara Dasa had great influence on Hindustani music. The foremost Hindustani musician Tansen’s teacher, Swami Haridas was Purandara Dasa’s disciple.
Tallapaaka Annamacharya, also popularly known as Annamayya (1408–1503AD), was a saint who composed songs in Telugu called ‘Sankirtanas’ in praise of lord Venkateswara.
Meanwhile, in the ensuing period between 1336AD – 1509AD the Vijayanagara empire emerged as a formidable empire ruling much of southern India and reached its peak by 1509AD.